Periodic table group 13 metal nitride crystals and method for manufacturing periodic table group 13 metal nitride crystals

ABSTRACT

A periodic table Group 13 metal nitride crystals grown with a non-polar or semi-polar principal surface have numerous stacking faults. The purpose of the present invention is to provide a period table Group 13 metal nitride crystal wherein the occurrence of stacking faults of this kind are suppressed. The present invention achieves the foregoing by a periodic table Group 13 metal nitride crystal being characterized in that, in a Qx direction intensity profile that includes a maximum intensity and is derived from an isointensity contour plot obtained by x-ray reciprocal lattice mapping of (100) plane of the periodic table Group 13 metal nitride crystal, a Qx width at 1/300th of peak intensity is 6×10 −4  rlu or less.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.14/502,249, filed Sep. 30, 2014, now allowed, which is a continuation ofInternational Application PCT/JP2013/059631, filed on Mar. 29, 2013, anddesignated the U.S., (and claims priority from Japanese PatentApplication 2012-081735 which was filed on Mar. 30, 2012 and JapanesePatent Application 2012-082153 which was filed on Mar. 30, 2012,) theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a periodic table Group 13 metal nitridecrystal and to a method of manufacturing a periodic table Group 13 metalnitride crystal. The invention relates in particular to a periodic tableGroup 13 metal nitride crystal in which the occurrence of stackingfaults is suppressed and to a method of manufacturing such a crystal.

BACKGROUND ART

A nitride semiconductor represented by gallium nitride has large bandgap, and interband transition is a direct transition. Therefore, thenitride semiconductor is a useful material for light emitting devices atrelatively short wavelength side such as ultraviolet, blue or greenlight emitting diodes and semiconductor lasers, and semiconductordevices such as electronic devices. Light-emitting devices are generallyproduced by growing a Group 13 metal nitride crystal in the periodictable on a substrate. And it is known that when Group 13 metal nitridecrystals in the periodic table are grown on different kinds ofsubstrates, light-emitting devices having a good efficiency cannot beprovided on account of the generation of stacking faults (see Non-patentDocuments 1-4), while high-performance light-emitting devices can beprovided when Group III metal nitride crystals in the periodic table arehomoepitaxially grown on an independent substrate of periodic tableGroup 13 metal nitride having no stacking faults (see Non-patentDocument 3). Hence, in order to provide high-performance light-emittingdevices, there exists a need to provide periodic table Group 13 metalnitride crystals which are free of crystal faults such as stackingfaults.

One typical method of producing a periodic table Group 13 metal nitridesubstrate entails the following. A crystal is homoepitaxially grown on aperiodic table Group 13 metal nitride seed having a polar plane such asthe (0001) plane as a principal plane, following which the crystal ismachined so that the desired plane emerges, thereby giving a periodictable Group 13 metal nitride substrate having a specific plane as theprincipal plane. For example, after GaN has been homoepitaxially grownon the (0001) plane of a GaN crystal seed, by polishing or cutting thecrystal so that the (10-10) plane emerges, it is possible to obtain aGaN semiconductor substrate in which the principal plane is the nonpolar(10-10) plane. GaN semiconductor substrates obtained by such a methodhave been confirmed to have few stacking faults (see Non-Patent Document2 and Non-Patent Document 5). However, in methods of growing a crystalon a seed in which the principal plane is a polar plane, one challengehas been the difficulty of providing a large-size semiconductorsubstrate in which the principal plane is a plane other than such polarplanes.

Compared with the foregoing method that makes use of a polar plane, verylittle literature exists on methods of homoepitaxially growing a crystalusing a periodic table Group 13 metal nitride seed in which theprincipal plane is not a polar plane.

For example, Patent Document 1 describes the approach of fittingtogether nitride semiconductor bars whose principal plane is the M planeby means of raised and recessed features provided on the C plane servingas the side wall, and growing a nitride semiconductor layer on theresulting array of nitride semiconductor bars.

Patent Document 2 describes a method of manufacturing a high-gradenitride semiconductor crystal having a non-polar plane of large surfacearea, which method entails growing the crystal in the +C-axis directionof a seed crystal.

In addition, Patent Document 3 describes an example where a GaNthin-film in which (10-10) plane serves as the principal plane was grownon (10-10) plane of a sapphire substrate, following which a 1.5 mm thickGaN crystal was grown by a liquid phase process. The same documentreports that the number of stacking faults in GaN crystals wherein the(10-10) plane served as the principal plane that were grown was 10⁴cm⁻¹.

In addition, Patent Document 4 describes growing a 3 mm-thick GaNcrystal by hydride vapor-phase epitaxy on a plurality of gallium nitride(GaN) crystal fragments in which the principal plane is a plane otherthan {0001} planes. Patent Document 5 describes growing a GaN crystal byhydride vapor-phase epitaxy on an underlying substrate having aprincipal plane with a misorientation angle relative to {1-100} planesof at least 4.1° and not more than 47.8°.

Patent Document 1: Japanese Patent Application Laid-open No. 2006-315947

Patent Document 2: Japanese Patent Application Laid-open No. 2008-308401

Patent Document 3: Japanese Patent Application Laid-open No. 2010-001209

Patent Document 4: Japanese Patent Application Laid-open No. 2010-013298

Patent Document 5: Japanese Patent Application Laid-open No. 2011-016676

Non-Patent Document 1: Applied Physics Express 1 (2008), 091102

Non-Patent Document 2: Phy. stat. sol. (a) 205, No. 5 (2008), 1056

Non-Patent Document 3: JJAP 46, No. 40 (2007), L960

Non-Patent Document 4: Appl. Phys. Lett. 91 (2007), 191906

Non-Patent Document 5: Applied Physics Express 2 (2009), 021002

DISCLOSURE OF THE INVENTION

As described above, although a method which homoepitaxially grows acrystal on a periodic table Group 13 metal nitride seed in which a polarplane serves as the principal plane, then cuts the crystal so that adesired plane emerges is able to obtain a periodic table Group 13 metalnitride substrate having few stacking faults, a large-size substratecannot be obtained. On the other hand, when the inventors investigatedthe method which involves homoepitaxially growing a crystal on aperiodic table Group 13 metal nitride seed in which a non-polar planesuch as (10-10) plane serves as the principal plane, then cutting fromthis a substrate in which the (10-10) plane serves as the principalplane, it became apparent for the first time that if an attempt is madeto produce a substrate by growing a thick-film crystal, the stackingfaults become extremely numerous. That is, in the course ofinvestigations by the inventors, it was found that when thick filmgrowth has been carried out, compared with a Group 13 metal nitridecrystal in the periodic table obtained by homoepitaxial growth on aperiodic table Group III metal nitride seed in which (0001) plane servesas the principal plane, a Group 13 metal nitride crystal in the periodictable obtained by homoepitaxial growth on a periodic table Group 13metal nitride seed in which (10-10) plane serves as the principal planehas many stacking faults.

In this way, it has not been possible with conventional methods toprovide periodic table Group 13 metal nitride crystals which have fewstacking faults and are moreover large in size.

Meanwhile, if it is possible to markedly suppress the generation ofstacking faults, particularly in directions parallel to the polar plane,when homoepitaxial growth has been carried out on the principal plane ofa substrate, it is thought that this would be extremely useful for theproduction of high-performing and high-efficiency light-emittingdevices. However, no methods for providing such periodic table Group 13metal nitride crystals have hitherto been proposed.

This invention provides, in a periodic table Group 13 metal nitridecrystal grown on a periodic table Group 13 metal nitride underlyingsubstrate having a non-polar or semi-polar plane as a principal plane, acrystal having few stacking faults, and also provides a method capableof manufacturing such a crystal.

The inventors have conducted extensive research in order to resolve theabove problems, focusing on reciprocal lattice mapping, which is onemethod of measurement using x-ray diffraction of a crystal. In thecourse of this work, the inventors found that the condition of stackingfaults within a crystal can be determined by (100) reciprocal latticemapping the crystal, deriving an intensity profile in the Qx directionthat includes a maximum intensity, and calculating the width at 1/300thof peak intensity. Moreover, on variously investigating the crystalgrowth conditions, the inventors realized that, even in a periodic tableGroup 13 metal nitride crystal grown on a periodic table Group 13 metalnitride underlying substrate, stacking faults can be reduced to a levelcomparable to that in a crystal grown using the C plane as the principalplane, in which it is generally regarded that stacking faults do notarise.

The inventors also found that, in x-ray rocking curve measurement forcrystals, the anisotropy of the crystal can be understood by comparingthe (100) rocking curve obtained when x-rays enter the crystalperpendicular to the a-axis with the (100) rocking curve obtained whenx-rays enter the crystal perpendicular to the c-axis, enabling thecondition of stacking faults within the crystal to be determined.Moreover, on variously investigating the crystal growth conditions, theinventors realized that, even in a periodic table Group 13 metal nitridecrystal grown on a periodic table Group 13 metal nitride underlyingsubstrate, stacking faults can be reduced to a level comparable to thatin a crystal grown using the C plane as the principal plane, in which itis generally regarded that stacking faults do not arise.

The inventors additionally found that by adjusting various growthconditions and thereby controlling the crystal growth mode, even in aperiodic table Group 13 metal nitride crystal grown on a periodic tableGroup 13 metal nitride underlying substrate, stacking faults can bereduced to a level comparable to that in a crystal grown using the Cplane as the principal plane, in which it is generally regarded thatstacking faults do not arise.

Thus, the present invention provides the followings:

[1] A periodic table Group 13 metal nitride bulk crystal that is aperiodic table Group 13 metal nitride crystal grown on a periodic tableGroup 13 metal nitride underlying substrate having a non-polar orsemi-polar plane as a principal plane,

the periodic table Group 13 metal nitride bulk crystal beingcharacterized in that, in a Qx direction intensity profile that includesa maximum intensity and is derived from an isointensity contour plotobtained by x-ray reciprocal lattice mapping of (100) plane of theperiodic table Group 13 metal nitride crystal, a Qx width at 1/300th ofpeak intensity is 6×10⁻⁴ rlu or less.

[2] The periodic table Group 13 metal nitride bulk crystal according to[1], characterized in that, in a Qx direction intensity profile thatincludes a maximum intensity and is derived from an isointensity contourplot obtained by x-ray reciprocal lattice mapping of (100) plane of theperiodic table Group 13 metal nitride crystal, a Qx width at 1/1000th ofpeak intensity is 1×10⁻³ rlu or less.

[3] A periodic table Group 13 metal nitride bulk crystal that is aperiodic table Group 13 metal nitride crystal grown on a periodic tableGroup 13 metal nitride underlying substrate having a non-polar orsemi-polar plane as a principal plane,

the bulk crystal being characterized in that a value calculated bydividing the width at 1/300th of peak intensity of a (100) rocking curveobtained when x-rays enter the periodic table Group 13 metal nitridecrystal perpendicular to the a-axis, by the width at 1/300th of peakintensity of a (100) rocking curve obtained when x-rays enter thecrystal perpendicular to the c-axis is 3 or less.

[4] The periodic table Group 13 metal nitride bulk crystal according to[3], characterized in that a value calculated by dividing the width at1/1000th of peak intensity of a (100) rocking curve obtained when x-raysenter the periodic table Group 13 metal nitride crystal perpendicular tothe a-axis, by the width at 1/1000th of peak intensity of a (100)rocking curve obtained when x-rays enter the crystal perpendicular tothe c-axis is 3 or less.

[5] The periodic table Group 13 metal nitride bulk crystal according to[3] or [4], characterized in that a value calculated by dividing thefull width at half peak intensity of the (100) rocking curve obtainedwhen x-rays enter the periodic table Group 13 metal nitride crystalperpendicular to the a-axis, by the full width at half peak intensity ofthe (100) rocking curve obtained when x-rays enter the crystalperpendicular to the c-axis is 4 or less.

[6] The periodic table Group 13 metal nitride bulk crystal according toany one of [1] to [5], characterized in that the number of stackingfaults visible in cathodoluminescence imaging is 3×10³/cm or less.

[7] The periodic table Group 13 metal nitride bulk crystal according toany one of [1] to [6], characterized in that a c-axis misorientationangle distribution at a distance of 40 mm is within ±0.5°.

[8] A substrate made of the periodic table Group 13 metal nitride bulkcrystal according to any one of [1] to [7].

[9] A semiconductor device, which uses the substrate according to [8].

Furthermore, another mode of the present invention provides thefollowings:

[10] A method of manufacturing a periodic table Group 13 metal nitridebulk crystal, comprising the step of growing, by a vapor-phase process,a periodic table Group 13 metal nitride layer on a periodic table Group13 metal nitride underlying substrate having a non-polar or semi-polarplane as a principal plane, the method being characterized in that, atan early stage of the growth step, the periodic table Group 13 metalnitride layer is two-dimensionally grown or step-flow grown.

[11] A method of manufacturing a periodic table Group 13 metal nitridebulk crystal, comprising the step of growing, by a vapor-phase process,a periodic table Group 13 metal nitride layer on a periodic table Group13 metal nitride underlying substrate having a principal plane that is aplane tilted at least 1.5° in the [0001] or [000-1] direction from the(10-10) plane, the method being characterized in that, in the growthstep, the periodic table Group 13 metal nitride layer is grown in anatmosphere where at least 40 volt of a total gas flow rate is an inertgas.

[12] The method of manufacturing a periodic table Group 13 metal nitridebulk crystal according to [10] or [11], characterized in that theprincipal plane of the underlying substrate is a plane tilted at least1.5° in the [000-1] direction from the (10-10) plane.

[13] The method of manufacturing a periodic table Group 13 metal nitridebulk crystal according to any one of [10] to [12], characterized in thatthe vapor-phase process is hydride vapor-phase epitaxy (HVPE).

[14] The method of manufacturing a periodic table Group 13 metal nitridebulk crystal according to any one of [10] to [13], characterized in thatthe underlying substrate is made of one single crystal of a periodictable Group 13 metal nitride.

[15] The method of manufacturing a periodic table Group 13 metal nitridebulk crystal according to any one of [10] to [14], characterized in thatgrowth temperature in the growth step is 1040° C. or below.

[16] The method of manufacturing a periodic table Group 13 metal nitridebulk crystal according to any one of [10] to [15], characterized inthat, in the growth step, a periodic table Group 13 source and anitrogen source are each fed as a gas and the density ratio of theperiodic table Group 13 source-containing gas (periodic table Group 13source gas) to the nitrogen source-containing gas (nitrogen source gas),expressed as “periodic table Group 13 source gas density/nitrogen sourcegas density,” is set to less than 1.

The periodic table Group 13 metal nitride crystal of the invention, inspite of having a non-polar or semi-polar plane as the principal plane,enables a good-quality periodic table Group 13 metal nitride crystalwith fewer stacking faults to be provided.

In addition, by using the method for producing Group 13 metal nitridecrystals in the periodic table according to the present invention, it ispossible to easily produce Group 13 metal nitride crystals in theperiodic table which are large in size and have few stacking faults andin which a non-polar plane or a semi-polar plane serves as the principalplane. By using, as a semiconductor substrate, the Group 13 metalnitride crystals in the periodic table thus produced and carrying outhomoepitaxial growth on a principal plane of the semiconductorsubstrate, it is possible to obtain a crystal which has few stackingfaults and in which stacking faults in directions parallel to a polarplane in particular have been markedly suppressed. As a result, byutilizing the present invention, it is possible to provide semiconductorlight-emitting devices having a high light-emitting intensity and anexcellent durability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the crystal growing system used inthe working examples of the invention.

FIG. 2 is a cathodoluminescence image of a crystal grown in a workingexample of the invention (photograph provided in place of diagram).

FIGS. 3A and 3B show scanning electron micrographs of the surfaces ofsamples produced in the reference working example (FIG. 3A) and thereference comparative example (FIG. 3B) (photographs provided in placeof diagram).

BEST MODE FOR CARRYING OUT THE INVENTION

The periodic table Group 13 metal nitride crystal of the invention andthe inventive method of manufacturing a periodic table Group 13 metalnitride crystal are described in detail below. The explanation ofconstituent elements may be made based on the representative embodimentof the present invention, but the present invention is not limited toonly such an embodiment.

Numerical range represented using “from . . . to” in the presentspecification means a range including the numerical values describedafter “from” and after “to” as a lower limit and an upper limit,respectively.

In this specification, when a Miller index is negative, the index ispreceded by a minus sign.

As used herein, < . . . > denotes a group of directions and [ . . . ]denotes an individual direction. Also, { . . . } denotes a group ofplanes and ( . . . ) denotes an individual plane.

Also, in the specification, “off angle” refers to an angle representingthe slippage of a given plane from an index plane.

In the present specification, “principal plane” is the largest(broadest) plane in the structure, and refers to the plane where crystalgrowth should be carried out. In this description of the presentapplication, the term “C plane” means the (0001) plane of a hexagonalstructure (wurtzite crystal structure), the plane being perpendicular tothe c axis. Such planes are polar planes; in a periodic table Group 13metal nitride crystal, the “+C plane” is the periodic table Group 13metal plane (in the case of gallium nitride, the gallium plane), and the“−C plane” is the nitrogen plane.

Moreover, in the specification, “M-plane” refers to planes which areequivalent to {1-100} plane, and refers specifically to (1-100) plane,(01-10) plane, (−1010) plane, (−1100) plane, (0-110) plane, or (10-10)plane, each of which is perpendicular to the m axis. Such planes arenon-polar planes, and are generally cleavage planes.

Moreover, in the specification, “A-plane” refers to planes which areequivalent to {2-1-10} plane, and refers specifically to (2-1-10) plane,(−12-10) plane, (−1-120) plane, (−2110) plane, (1-210) plane, or (11-20)plane, each of which is perpendicular to the a axis. Such planes arenon-polar planes.

Further, in this specification, “c axis,” “m axis” and “a axis” refer toaxes that are perpendicular to, respectively, a C plane, an M plane andan A plane.

Furthermore, in the specification, “semi-polar plane” refers to, in acase where the Group 13 metal nitride crystal in the periodic table is ahexagonal crystal whose principal plane is represented as (hklm), forexample, a plane where at least two from among h, k and l are not 0, andm is not 0. Also, a semi-polar plane refers to a plane which is tiltedwith respect to a C plane such as (0001) plane, and which, in caseswhere both a Group 13 element in the periodic table and nitrogen arepresent at the surface or only one of these is present, has an abundanceratio therebetween which is not 1:1. Also, h, k, l and m are eachindependently any integer which is preferably from −5 to 5, and morepreferably from −3 to 3, and the semi-polar plane is preferably alow-index plane. Specific examples include low-index planes such as{20-21} planes, {20-2-1} planes, {30-31} planes, {30-3-1} planes,{10-11} planes, {10-1-1} planes, {10-12} planes, {10-1-2} planes,{11-22} planes, {11-2-2} planes, {11-21} planes and {11-2-1} planes.

The periodic table Group 13 metal nitride crystal of the invention is aperiodic table Group 13 metal nitride crystal obtained by growing aperiodic table Group 13 metal nitride semiconductor layer on a periodictable Group 13 metal nitride underlying substrate having a non-polar orsemi-polar plane as a principal plane. The principal plane of theperiodic table Group 13 metal nitride crystal that has been grown ispreferably a non-polar plane or a semi-polar plane. Examples ofnon-polar planes include {11-20} planes and {10-10} planes, with {10-10}planes being preferred. Preferred semi-polar planes include planes forwhich the normal vector is tilted by an angle of at least 5° and notmore than 50° in the c-axis direction from a {10-10} plane. Of these,planes tilted by an angle of at least 6° and not more than 30° are morepreferred, and planes tilted by an angle of at least 7° and not morethan 15° are even more preferred. Other preferred semi-polar planesinclude planes tilted by an angle at least 5° and not more than 50° inthe a-axis direction from a {10-10} plane, with planes tilted by anangle of at least 10° and not more than 40° being more preferred, andplanes tilted by an angle of at least 15° and not more than 35° beingstill more preferred. Specifically, {30-31} planes, {30-3-1} planes,{20-21} planes, {20-2-1} planes, {10-11} planes, {10-1-1} planes,{40-41} planes, {40-4-1} planes, {50-51} planes and {50-5-1} planes aremore preferred, with {30-31} planes, {30-3-1} planes, {20-21} planes,{20-2-1} planes, {10-11} planes and {10-1-1} planes being still morepreferred.

This invention provides, in a periodic table Group 13 metal nitridecrystal produced by crystal growth using a non-polar or semi-polar planeas the principal plane, in which growth numerous stacking faults havehitherto formed, a periodic table Group 13 metal nitride crystal havingfewer stacking faults.

The periodic table Group 13 metal nitride crystal of the invention ischaracterized in that, in a Qx direction intensity profile that includesa maximum intensity and is derived from an isointensity contour plotobtained by x-ray reciprocal lattice mapping of the (100) plane of thecrystal, the Qx width at 1/300th of peak intensity (Qx_(1/300)) is6×10⁻⁴ rlu or less.

X-ray reciprocal lattice mapping is one type of measurement that usesx-ray diffraction to measure crystallinity and the state of latticestrain. The inventors have discovered that by x-ray reciprocal latticemapping the (100) plane of a crystal, stacking faults within the crystalcan be understood.

Specifically, when the Qx direction intensity profile that includes amaximum intensity and is derived from an isointensity contour plotobtained by x-ray reciprocal lattice mapping the (100) plane of thecrystal is plotted onto a graph of the Qx direction as the abscissa andthe intensity as the ordinate, a curve in the shape of a peak, ormountain, appears. Upon examining the Qx width at 1/300th the maximumintensity of this peak (the peak intensity), the inventors havediscovered that crystals in which this Qx width is 6×10⁻⁴ rlu or lessare crystals having few stacking faults.

In x-ray reciprocal lattice mapping the (100) plane of the crystal, thex-rays enter the crystal from a direction orthogonal to the a-axis,making it easy to understand basal plane stacking faults, which arestacking defects in the c-axis direction. Hence, in this invention, thex-ray reciprocal lattice mapping of the (100) plane of the crystal iscarried out.

Also, in an isointensity contour plot obtained by reciprocal latticemapping, because an x-ray 2θ−ω two-axis scan is measured in angularsteps of 0.005° for both 2θ and ω over a measurement angle range of 1°,the measurement step (measurement width) in the Qy direction becomes3×10⁻³ rlu, and the Qx direction intensity in this measurement widthappears. By deriving from this an intensity profile in the Qx directionthat includes the maximum intensity, precise measurement of theintensity is possible.

By taking the derived profile and plotting it on a graph of the Qxdirection as the abscissa and the intensity as the ordinate, the profilebecomes a peak-shaped curve, and the Qx width at 1/300th of peakintensity is measured.

The Qx width at 1/300th of peak intensity, when measured, is 6×10⁻⁴ rluor less. Hence, the periodic table Group 13 metal nitride crystal of theinvention can be regarded as a crystal in which stacking faults havebeen suppressed. This Qx width is preferably not more than 4×10⁻⁴ rluand more preferably not more than 3×10⁻⁴ rlu.

Preferably, the periodic table Group 13 metal nitride crystal of theinvention has, in the Qx direction intensity profile that includes amaximum intensity and is derived from an isointensity contour plotobtained by x-ray reciprocal lattice mapping the (100) plane of thecrystal, a Qx width at 1/1000th (Qx_(1/1000)) of peak intensity of1×10⁻³ rlu or less. This Qx width is preferably not more than 7×10⁻⁴ rluand more preferably not more than 5×10⁻⁴ rlu.

The inventors have confirmed that the Qx width at 1/300th of peakintensity (Qx_(1/300)) and the Qx width at 1/1000th of peak intensity(Qx_(1/1000)) show a high correlation with the absence or presence ofstacking faults.

The full width at half maximum (FWHM) is often used in the evaluation ofcurves having a peak-like shape. However, the inventors, having observedthat the FWHM of the Qx profile also reflects at the same time theinfluence of dislocations other than stacking faults, have found as aresult that the correlation with the stacking fault density is notalways good. By contrast, the spectral width at the foot of thepeak-shaped curve created by taking a profile of Qx was found tocorrelate well with the stacking fault density.

Qx width of the present invention is measured as follows.

Generally, in reciprocal lattice mapping measurement, 2θ is set at agiven value and rocking curve (ω scan) measurement is carried out, thena small change is made in the 2θ value and rocking curve measurement isagain carried out, this process being carried out repeatedly. In sodoing, a high angular resolution for 2θ and ω is desirable. Hence, it isdesirable for an x-ray mirror or a two-crystal monochromator and afour-crystal monochromator, or for a combination of these, to bedisposed on the incident x-ray side so that parallelism andmonochromaticity of the incoming x-rays is achieved. It is alsodesirable to place a so-called analyzer crystal on the detector side.Alternatively, as with measurement in the working examples of thisinvention, a one-dimensional array-type semiconductor device having ahigh angular resolution may be used as the detector. Using such an x-raydiffraction apparatus, first, x-rays are made to enter the crystal in adirection perpendicular to the a-axis and (100) plane reciprocal latticemapping is carried out. Also, to eliminate the influence of curvature(warpage) of the crystal plane on the diffraction peak, it is necessaryto suitably narrow, using a slit or the like, the x-ray beam diameter inthe directions orthogonal to the w rotational axis. Intensity mapping inthe resulting 2θ−ω space is converted to intensity mapping in the Qx-Qyspace. An intensity line profile in the Qx direction which passesthrough the maximum value in the Qy direction is derived from thereciprocal lattice mapping data thus obtained, giving the Qx width. Inthis invention, an x-ray 2θ−ω two-axis scan can be measured in angularsteps of 0.005° for both 2θ and ω over a measurement angle range of 1°.

The intensity in the resulting Qx direction intensity profile thatincludes a maximum intensity and is derived from the isointensitycontour plot is examined and the above-mentioned 1/300th and 1/1000thintensity values are calculated.

A crystal wherein the Qx_(1/300) and Qx_(1/1000) values for the periodictable Group 13 metal nitride crystal of the invention fall within theabove ranges can be obtained by employing two-dimensional growth orstep-flow growth as the crystal growing mode. More specifically, thiscan be achieved by growing the crystal at a relatively low temperatureat the initial stage of growth (0 to 15 minutes) and/or during the mainstage of crystal growth, by using an inert gas as the carrier gas frombefore the start of the reaction until growth is complete, or by havingthe misorientation angle of the principal plane of the underlyingsubstrate fall in a given range. By employing such conditions, warpageof the crystal planes also tends to become smaller.

The same can be achieved as well by carrying out, in crystal growth,lateral growth that causes the crystal to grow in a directionperpendicular to the direction in which the crystal thickness increasesfor the crystal as a whole, and collecting the regions that have formedby lateral growth after removing the seed crystal, regions that haveformed on the principal plane of the seed crystal and regions that haveformed by lateral growth from sidewalls of the seed crystal. Lateralgrowth can be controlled by means of such parameters as temperature,source gas partial pressure, nitrogen source/periodic table Group 13metal source ratio, and source gas feed port-crystal growth enddistance. In lateral crystal growth, the gas addition time at the startof growth is generally at least 10 seconds, preferably at least 20seconds, and more preferably at least 30 seconds, and is generally notmore than 10 minutes, preferably not more than 5 minutes, and morepreferably not more than 2 minutes.

The periodic table Group 13 metal nitride crystal according to anotheraspect of the invention is characterized in that a value calculated bydividing the width at 1/300th of peak intensity of a (100) rocking curveobtained when x-rays enter the periodic table Group 13 metal nitridecrystal perpendicular to the a-axis, by the width at 1/300th of peakintensity of a (100) rocking curve obtained when x-rays enter thecrystal perpendicular to the c-axis is 3 or less, preferably 2 or less,and more preferably 1.5 or less.

A value calculated by dividing the width at 1/1000th of peak intensityof a (100) rocking curve obtained when x-rays enter the periodic tableGroup 13 metal nitride crystal perpendicular to the a-axis, by the widthat 1/1000th of peak intensity of a (100) rocking curve obtained whenx-rays enter the crystal perpendicular to the c-axis is 3 or less,preferably 2 or less, and more preferably 1.5 or less.

A value calculated by dividing the full width at half peak intensity ofthe (100) rocking curve obtained when x-rays enter the periodic tableGroup 13 metal nitride crystal perpendicular to the a-axis, by the fullwidth at half peak intensity of the (100) rocking curve obtained whenx-rays enter the crystal perpendicular to the c-axis is 4 or less,preferably 3 or less, and more preferably 2 or less.

In a periodic table Group 13 metal nitride crystal according to yetanother aspect of the invention, by setting the ratio between therespective widths at 1/300th of peak intensity to a specific value whenx-rays enter the crystal perpendicular to the a-axis and when x-raysenter the crystal perpendicular to the c-axis in x-ray rocking curvemeasurement of the (100) plane, a crystal having fewer stacking faultscan be provided. It appeared conceivable that the rocking curve valuesthus measured when x-rays enter a periodic table Group 13 metal nitridecrystal perpendicular to the a-axis and when x-rays enter the crystalperpendicular to the c-axis express the anisotropy of the crystal.Hence, the inventors realized that, in cases where the value calculatedby dividing the width at 1/300th of peak intensity of a (100) rockingcurve obtained when x-rays enter the periodic table Group 13 metalnitride crystal perpendicular to the a-axis by the width at 1/300th ofpeak intensity of a (100) rocking curve obtained when x-rays enter theperiodic table Group 13 metal nitride crystal perpendicular to thec-axis is 3 or less, that is, in cases where the crystal anisotropy issmall, the number of stacking faults in the crystal obtained is reduced.

The periodic table Group 13 metal nitride crystal in still anotheraspect of the invention has a value calculated by dividing the width at1/1000th of peak intensity of a (100) rocking curve obtained when x-raysenter the periodic table Group 13 metal nitride crystal perpendicular tothe a-axis by the width at 1/1000th of peak intensity of a (100) rockingcurve obtained when x-rays enter the crystal perpendicular to the c-axiswhich is preferably 3 or less, or has a value obtained by dividing thefull width at half of the peak intensity of a (100) rocking curveobtained when x-rays enter the periodic table Group 13 metal nitridecrystal perpendicular to the a-axis by the full width at half of thepeak intensity of a (100) rocking curve obtained when x-rays enter theperiodic table Group 13 metal nitride crystal perpendicular to thec-axis which is preferably 4 or less.

Because x-ray rocking curve measurement is a method that can be measuredmore easily than the above-described Qx_(1/300) and Qx_(1/1000), itallows one to determine, by measurement of the crystal anisotropy insuch x-ray rocking curve measurement, whether the Qx_(1/300) andQx_(1/1000) of this invention are in the ranges of the invention.

It is preferable for the periodic table Group 13 metal nitride crystalof the invention to have not more than 1×10³/cm basal plane stackingfaults that are actually visible under cathodoluminescence imaging.Periodic table Group 13 metal nitride crystals which satisfy theQx_(1/300) condition of this invention are, as noted before, crystals inwhich the number of basal plane stacking faults has been reduced; thenumber of basal plane stacking faults visible in cathodoluminescenceimaging tends to be 3×10³/cm or less. This Qx width is preferably notmore than 1×10³/cm and more preferably not more than 2×10²/cm.

The periodic table Group 13 metal nitride crystal according to anotheraspect of the invention has a value calculated by dividing the width at1/300th of peak intensity of a (100) x-ray rocking curve by the width at1/300th of peak intensity of a (300) x-ray rocking curve which ispreferably 1.5 or less, more preferably 1.0 or less, and even morepreferably 0.5 or less. By setting the value to the above upper limit orless, a crystal having fewer stacking faults can be provided. Theincident direction of the x-rays at this time is made perpendicular tothe a-axis.

Because stacking faults are planar defects that exist parallel to the(0001) plane (i.e., the C plane), which is a polar plane, by examining across-section that intersects the polar plane (especially across-section perpendicular to the polar plane), the stacking faults canbe confirmed as linear bright lines. The stacking faults can be observedby examining the crystal surface with a fluorescence microscope or bylow-temperature cathodoluminescence (CL) imaging at 100 K or below.Specifically, by producing a LED structure that emits 405 nm light atthe crystal surface where one wishes to observe stacking faults andexamining an image of this surface with a fluorescence microscope,stacking fault sites can be seen as bright lines. Also, the stackingfaults in low-temperature CL appear as dark lines in wavelengthresolution imaging with the wavelength fixed at the near band-edgeluminescence wavelength (in an undoped layer obtained by metal organicchemical vapor deposition (MOCVD), this is generally the wavelength ofneutral donor bound exciton emission), and appear as bright lines inwavelength resolution imaging with the wavelength fixed at the peak(approximately 364 nm) of emission from basal plane stacking faults.Those lines having a length of at least 5 μm in the a-axis directionthat are observed at the surface in particular are treated in thisinvention as stacking faults.

The periodic table Group 13 metal nitride crystal of the invention has aratio of 3.41 eV peak intensity from stacking faults I(BSF) to 3.47 eVpeak intensity from band-edge luminescence I(D⁰X_(A)) (the intensitieshere being low-temperature PL intensities), expressed asI(BSF)/I(D⁰X_(A)), which is preferably 0.1 or less, more preferably 0.01or less, and even more preferably 0.005 or less. Furthermore, threadingdislocation density of the Group 13 metal nitride crystals in theperiodic table of the present invention is preferably 10⁸/cm² or less,more preferably 10⁷/cm² or less, even more preferably 10⁶/cm² or less.

Generally, in cases where a periodic table Group 13 metal nitride layerof the same type as the underlying substrate has been grown by a processsuch as hydride vapor-phase epitaxy (HVPE) on an underlying substratethat has a non-polar or semi-polar plane as the principal plane and wasfabricated by slicing at a specific angle or in a specific direction acrystal obtained by crystal growth in the c-axis direction on the Cplane, the number of stacking faults intrinsic to the grown crystal ishigher than the number of stacking faults intrinsic to the underlyingsubstrate. For example, in the underlying substrate, the number ofstacking faults is small and the bright lines observed are short, and sothe bright line density is small. However, in the grown crystal, thenumber of stacking faults increases and the bright lines observed arelonger, and so the bright line density is larger. Hence, as the growthof periodic table Group 13 metal nitride layer proceeds, the stackingfaults expand, and it is thought to be possible that faults not observedin the seed crystal will newly emerge in the periodic table Group 13metal nitride layer. When carrying out thick-film growth, the rise inthe number of stacking faults has posed a serious problem.

In the periodic table Group 13 metal nitride crystals of this invention,warpage of the crystal planes tends to limited. Specifically, themisorientation angle distribution at a distance of 40 mm is preferablywithin ±1°, with a misorientation angle distribution within ±0.5° beingmore preferred.

For example, when the misorientation angle distribution in the c-axisdirection is measured for a sample in which the M plane is the principalplane, x-rays are made to enter the sample perpendicular to the a-axisand a x-ray rocking curve of, for example, the (100) plane is measuredat numerous points at set intervals along the c-axis direction. Theamount of change in ω per unit length is determined from therelationship between the measurement positions and the ω peak. Fromthis, it is possible to determine the misorientation angle distributioncorresponding to a distance of 40 mm. Yet, in the case of a crystalhaving a size such that the maximum length of the principal plane isabout several hundred microns, because the crystal is small comparedwith the beam size in an ordinary x-ray system, the measurementsdescribed above are difficult to carry out. However, by employing anx-ray source which uses emitted light generated with an accelerator, abeam having a diameter on the order of several microns can be obtained,thus enabling measurement of the misorientation angle distribution perunit length within crystals of the above sizes. It is possible in thisway to determine the misorientation angle distribution corresponding toa distance of 40 mm.

Thus, the periodic table Group 13 metal nitride crystal of the inventionis a crystal having a reduced number of stacking faults and littlecrystal lattice warpage. In the practice of this invention, in periodictable Group 13 metal nitride crystals grown with a non-polar orsemi-polar plane as the principal plane, it is possible to providecrystals having a reduced number of stacking faults.

The periodic table Group 13 metal nitride crystal of the invention is acrystal grown on a periodic table Group 13 metal nitride underlyingsubstrate having a non-polar or semi-polar plane as the principal plane,although the underlying substrate is otherwise not particularly limited,provided it is made of a periodic table Group 13 metal nitride. Examplesof kinds of Group 13 metal nitrides in the periodic table includegallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), andmixed crystals thereof. It is especially preferable to select a seedcrystal made of the same type of periodic table Group 13 metal nitrideas the periodic table Group 13 metal nitride crystal of the invention.For example, in cases where the periodic table Group 13 metal nitridecrystal is gallium nitride (GaN), an underlying substrate made ofgallium nitride (GaN) is used. However, it is not necessary for the basesubstrate and the periodic table Group 13 metal nitride layer to have acompletely identical composition; so long as the compositions are atleast 99.75% (atomic ratio) in agreement, they may be regarded here asbeing the same kind of Group 13 metal nitrides in the periodic table.For example, in a case where a periodic table Group 13 metal nitridelayer doped with silicon, oxygen or the like is grown on a seed crystalcomposed of GaN, this is regarded as growing the same kind of Group 13metal nitride in the periodic table and is thus referred to ashomoepitaxial growth.

The size of the principal plane of the underlying substrate may besuitably selected according to the size of the target periodic tableGroup 13 metal nitride crystal, although the surface area of theprincipal plane is preferably at least 2.5 cm², and more preferably atleast 20 cm².

In the practice of the invention, aside from using one single crystal ofa periodic table Group 13 metal nitride as the underlying substrate, itis also possible for a plurality of periodic table Group 13 metalnitride seed crystals to be used in combination as the underlyingsubstrate. In one example of a method that may be used, plates having anon-polar or semi-polar plane as the principal plane are cut out as seedcrystals from a periodic table Group 13 metal nitride crystal having theC plane as the principal plane, and a plurality of these seed crystalsare arranged to form the underlying substrate (this is referred to asthe “tile method”). In another example, a single periodic table Group 13metal nitride crystal having a non-polar or semi-polar plane as theprincipal plane (which crystal is referred to below as the “motherseed”) is produced from a larger crystal than those obtained by the tilemethod, and is used as the underlying substrate. With these methods,even in cases where a large underlying substrate cannot be furnished forcrystal growing, it is possible to obtain a periodic table Group 13metal nitride crystal having a large surface area. So long as theprincipal plane of the underlying substrate formed by arranging togethera plurality of seed crystals is a non-polar or semi-polar plane overall,it may be either heterogeneous or homogeneous in-plane.

The tile method includes the steps of preparing a plurality of seedcrystals having a non-polar or semi-polar plane as the principal plane,arranging together the plurality of seed crystals, and growing aperiodic table Group 13 metal nitride crystal on the seed crystals.

The method that uses a mother seed includes the steps of furnishing aplurality of seed crystals having a non-polar or semi-polar plane as theprincipal plane, arranging together the plurality of seed crystals,growing a periodic table Group 13 metal nitride layer on the seedcrystals, producing a mother seed having a non-polar or semi-polar planeas the principal plane from the resulting periodic table Group 13 metalnitride semiconductor layer, and growing a periodic table Group 13 metalnitride crystal on the mother seed.

Seed crystals having the same index plane or a combination of seedcrystals having different index planes may be used as the plurality ofseed crystals. When arranging together a plurality of seed crystals, theseed crystals are arranged so that the crystal orientations are on thesame plane, with neighboring seed crystals either in mutual contact ornot in contact. Because “crystal orientation” refers here to theinclination of the direction of the normal to the principal plane ineach seed crystal, aligning the crystal orientations means to align theoff angles among the seed crystals.

In particular, to achieve uniformity in the resulting Group 13 metalnitride crystals in the periodic table, the principal planes among theseed crystals have a distribution of plane directions that is preferablywithin ±5°, more preferably within ±3°, even more preferably within +1°,and most preferably within ±0.5°. Because “plane direction” refers tothe inclination of the direction of the normal to the principal plane ineach seed crystal, a distribution of plane directions being within ±5°means the same thing as an off-angle being within ±5°.

The method for arranging a plurality of seed crystals is notparticularly limited; the seed crystals may be arranged next to eachother on the same flat surface or they may be arranged next to eachother by planar stacking. In cases where the principal planes of theplurality of seed crystals have differing plane directions, arrangingthe seeds so that the plane directions of their respective principalplanes face in the same direction is preferred because the Group 13metal nitride crystals in the periodic table obtained tends to have agood crystallinity over seed crystal junctions. Also, when a pluralityof seed crystals are arranged, it is preferable for the directions ofthe lines of intersections between the principal plane and the polarplane for the respective seed crystals to be aligned. Moreover, thedistribution in the directions of the lines of intersection between theprincipal plane and the polar plane for the respective seed crystals isset to preferably within +5°, more preferably within ±3°, even morepreferably within ±1°, and particularly preferably within +0.5°.

So long as the periodic table Group 13 metal nitride crystal of theinvention is a crystal that satisfies the essential features describedabove, the method of manufacture is not particularly limited. Forexample, manufacture may be carried out by a method that includes as thecrystal growing step a known crystal growing method such as:

-   (1) hydride vapor-phase epitaxy (HVPE);-   (2) metal organic chemical vapor deposition (MOCVD);-   (3) metal organic chloride vapor phase growth (MOC);-   (4) sublimation;-   (5) liquid phase epitaxy (LPE); and-   (6) ammonothermal growth.    The periodic table Group 13 metal nitride crystal of the invention    is preferably manufactured using a vapor phase process such as (1)    to (4) above. From the standpoint of mass productivity, the use of    the HVPE or MOCVD is preferred, with the use of HVPE being    especially preferred.

Although no particular limitation is imposed on the specific crystalgrowing conditions (in the crystal growing step), a periodic table Group13 metal nitride crystal that satisfies the above-described essentialfeatures of the invention can be manufactured by the initial stage ofcrystal growth proceed by two-dimensional growth or step-flow growth.

Crystal growth modes for initial growth of the periodic table Group 13metal nitride layer include the three-dimensional growth mode, thetwo-dimensional growth mode and the step-flow growth mode. It isapparent from studies done by the inventors that there is a possibility,in the three-dimensional growth mode, of island-like periodic tableGroup 13 metal nitride crystals growing as seed crystals on theunderlying substrate and of island-like (three-dimensional) growthproceeding, resulting in the introduction of a large amount of faultswhen the islands coalesce. Hence, when growing the periodic table Group13 metal nitride layer on the underlying substrate, particularly at theinitial stage of growth, by employing growth conditions that increasethe wettability of the starting materials with respect to the underlyingsubstrate and by promoting a two-dimensional growth or step-flow growthmode, a high-quality periodic table Group 13 metal nitride crystalhaving a reduced number of stacking faults can be obtained even in caseswhere thick-film formation has been carried out. The specific period ofinitial growth (initial stage of crystal growth) is not particularlylimited, and may represent, for example, a period of from 1 to 30minutes from the start of crystal growth.

Other than the above-described method involving two-dimensional growthor step-flow growth, by utilizing lateral growth which entails havingcrystal growth proceed in a direction perpendicular to the direction ofcrystal growth (the direction of increasing crystal thickness for thecrystal as a whole), it is possible to obtain a periodic table Group 13metal nitride crystal which satisfies the essential features of theinvention. Specifically, such a crystal can be obtained by removing,from a crystal grown in such a way that lateral growth also proceeds,regions that have formed on the principal plane of the underlyingsubstrate and regions that have formed by lateral growth from sidewallsof the underlying substrate, and collecting the regions that have formedon top of the regions formed by lateral growth from sidewalls of theunderlying substrate. That is, the crystal that has formed on a regionformed by lateral growth can become a periodic table Group 13 metalnitride crystal which satisfies the essential features of the invention.Lateral growth can be controlled by means of parameters such astemperature, source gas partial pressure, nitrogen source/periodic tableGroup 13 metal source ratio, and source gas feed port-crystal growth enddistance. However, in the case of lateral growth, the gas addition timeat the initial stage of growth is generally at least 10 seconds,preferably at least 20 seconds, and more preferably at least 30 seconds,and is generally not more than 10 minutes, preferably not more than 5minutes, and more preferably not more than 2 minutes.

The manufacturing method for obtaining the periodic table Group 13 metalnitride crystal of the invention is preferably a method that carries outtwo-dimensional growth or step-flow growth, that is, a method (referredto below as “Manufacturing Method 1”) which includes the step ofgrowing, by a vapor phase process, a periodic table Group 13 metalnitride layer on a periodic table Group 13 metal nitride underlyingsubstrate having a non-polar or semi-polar plane as the principal plane,wherein, at the initial stage of the growth step, the periodic tableGroup 13 metal nitride layer is two-dimensionally grown or step-flowgrown.

The growth step may be one in which growth occurs also on planes otherthan the principal plate of the underlying substrate. Moreover, thegrowth step, providing it is growth on the principal plane of the basesubstrate, need not necessarily involve growth in a directionperpendicular to the principal plane. Also, the direction of growth maychange in the course of the growth step.

The thickness of the crystal grown on the principal plane of the basesubstrate may be suitably selected according to, for example, the sizeof the Group 13 metal nitride crystals in the periodic table that oneultimately wishes to obtain. With such a production method, theformation and expansion of stacking faults can be suppressed, enablingthe thickness of the crystal grown on the principal plane of theunderlying substrate to be made, for example, 1 mm or more, preferably 3mm or more, and more preferably 10 mm or more. The crystal thickness ispreferably not more than 51 mm, more preferably not more than 24 mm, andeven more preferably not more than 14 mm. As used herein, “thickness”refers to the thickness in the direction perpendicular to the principalplane of the underlying substrate.

Two-dimensional growth or step-flow growth in the initial stage ofcrystal growth can be achieved by selecting conditions such as (a) to(d) below.

-   (a) Using an underlying substrate in which the principal plane is    the (10-10) plane or a plane tilted at least 1.5° in the [0001] or    [000-1] direction from the (10-10) plane.-   (b) Growing the crystal in an atmosphere in which at least 40 vol %    of the total gas flow rate is inert gases.-   (c) Growing the crystal at a growth temperature not higher than    1040° C.-   (d) When introducing gases into the system at the start of growth,    setting the time required until the predetermined gas flow rate is    achieved (referred to below as “gas introduction time”) to not more    than 10 minutes.

These conditions may be used alone or may be used in combination. Ofthese, employing a combination of (a) and (b) is preferred. It is alsopreferable to combine (c) and (d) with these.

Up until now, in cases where the growth of a periodic table Group 13metal nitride crystal was carried out by HVPE using an underlyingsubstrate having a polar plane as the principal plane, when an inert gassuch as nitrogen was used as the carrier gas, a large amount ofpolycrystal adhered to the interior of the reactor, causing reactordeterioration or adversely affecting the crystallinity. Hence, hydrogenor the like has generally been used as the carrier gas. However, it hasbecome apparent from investigations by the inventors that, surprisingly,when use is made of an underlying substrate in which a planarorientation other than a polar plane is the principal plane, theformation and propagation of stacking faults can be suppressed bycarrying out crystal growth in an atmosphere in which at least 40 vol %of the total gas flow rate is inert gases. In addition, when the (10-10)plane serves as the principal plane of the underlying substrate, byimparting to this a specific misorientation angle, not only can thenumber of stacking faults within the resulting crystal be reduced, it ispossible as well to effectively suppress the formation of polycrystalthat has hitherto been a problem.

The above conditions (a) to (d) are described below in greater detail.

-   (a) Using an underlying substrate in which the principal plane is    the (10-10) plane or a plane tilted at least 1.5° in the [0001] or    [000-1] direction from the (10-10) plane.

In this invention, the principal plane of the underlying substrate is anon-polar plane or a semi-polar plane. However, in order to havetwo-dimensional growth or step-flow growth proceed more easily, anunderlying substrate in which the principal plane is a plane tilted atleast 1.5° in the [0001] or [000-1] direction from the (10-10) plane, anon-polar plane, is preferred. The angle of tilt from the (10-10) planeis sometimes referred to as the misorientation angle. The misorientationangle of the underlying substrate is preferably at least 1.5°, morepreferably at least 1.75°, and even more preferably at least 2.0°, butis preferably not more than 30°, more preferably not more than 15°, andeven more preferably not more than 10°. The direction of tilt from the(10-10) plane is preferably [000-1]. Preferred planar orientations forthe principal plane are {20-21} planes, {20-2-1} planes, {30-31} planes,{30-3-1} planes, {10-11} planes, {10-1-1} planes, {10-12} planes,{10-1-2} planes, {11-22} planes, {11-2-2} planes, {11-21} planes and{11-2-1} planes.

-   (b) Growing the crystal in an atmosphere in which at least 40 vol %    of the total gas flow rate is inert gases.

In the growth step, growing the periodic table Group 13 metal nitridelayer in an atmosphere in which at least 40 vol % of the total gas flowrate is inert gases makes it easier for two-dimensional growth orstep-flow growth at the initial stage of the growth step to proceed,enabling the formation and expansion or propagation of stacking faultsto be suppressed. Setting the proportion of inert gases included in thetotal gas flow rate to at least 70 vol % is preferred, and setting thisto at least 90 vol % is more preferred. The proportion of inert gasincluded in the total gas flow rate can be calculated from the sum ofthe flow rates of all the inert gases that have been passed through thereactor relative to the sum of the flow rates of all the gases that havebeen passed through the reactor.

-   (c) Growing the crystal at a growth temperature not higher than    1040° C.

Having the growth temperature in the growth step be a relatively lowtemperature makes it easier for the two-dimensional growth or step-flowgrowth to proceed at the initial stage of the growth step, and enablesthe formation and expansion or propagation of stacking faults to besuppressed. In particular, it suffices for the growth temperature at theinitial stage of the growth step to be a low temperature, and isacceptable to raise the temperature in the course of the growth step.Specifically, the temperature thereof is preferably 1040° C. or less,more preferably 1000° C. or less, even more preferably 980° C. or less.

-   (d) When introducing gas at the start of growth, setting the time    required until the predetermined gas flow rate is achieved (referred    to below as “gas introduction time”) to not more than 10 minutes.

When gas is introduced at the start of growth, by having the timerequired until the predetermined gas flow rate is achieved be arelatively short time, it is possible to carry out the desired growthfrom the start of growth, enabling the formation and expansion orpropagation of stacking faults to be suppressed. The time thereof ispreferably 10 minutes or less, more preferably 5 minutes or less, evenmore preferably 2 minutes or less.

The method of manufacture for obtaining the periodic table Group 13metal nitride crystal of the invention is most preferably amanufacturing method which combines above conditions (a) and (b); thatis, a manufacturing method that includes the step of growing a periodictable Group 13 metal nitride layer by a vapor phase process on aperiodic table Group 13 metal nitride underlying substrate having as theprincipal plane a plane tilted at least 1.5° in the [0001] or [000-1]direction from the (10-10) plane, and a manufacturing method which, inthe crystal growing step, grows a periodic table Group 13 metal nitridelayer in an atmosphere in which at least 40 volt of the total gas flowrate is inert gases (referred to below as “Manufacturing Method 2”).

Hereafter in this specification, the phrase “manufacturing method of theinvention” shall be understood to include above Manufacturing Method 1and Manufacturing Method 2, and to collectively refer to both.

For the sake of illustration, a crystal growing method which uses HVPEis described below together with the manufacturing apparatus, but itshall be understood that the crystal growing step in the inventivemanufacturing method is not limited to this example, and the use of theother crystal growing methods mentioned above is also possible.

<Production Equipment and Production Conditions>

1) Basic Structure

FIG. 1 is a schematic diagram of a manufacturing apparatus which may beemployed in a manufacturing method that uses HVPE. The HVPE equipmentillustrated in FIG. 1 includes, within a reactor 100: a susceptor 107for loading a base substrate (seed), and a reservoir 105 which ischarged with a starting material for the Group 13 metal nitride crystalsin the periodic table to be grown. The apparatus is provided withintroduction tubes 101 to 104 for introducing a gas into the reactor 100and an exhaust tube 108 for exhaustion. The apparatus is furtherprovided with a heater 106 for heating the reactor 100 from a side.

2) Reactor Material, and Types of Atmospheric Gases

Quartz, sintered born nitride, stainless steel and the like are used asa material of the reactor 100. Preferred material is quartz. Atmospheregas is charged in the reactor 100 in advance of initiation of thereaction. The atmosphere gas (carrier gas) can include a gas such ashydrogen, nitrogen, He, Ne or Ar.

Of these, to manufacture high-quality periodic table Group 13 metalnitride crystal having a low stacking fault density, using an inert gassuch as nitrogen, helium, neon or argon as the ambient gas is preferred,with the use of nitrogen (N₂) being more preferred. Those gases may beused singly or as mixtures thereof. When an inert gas is used as theambient gas, the content of inert gas in the ambient gas is preferablyat least 40 vol %, more preferably at least 70 vol %, and even morepreferably at least 90 vol %.

Setting the ambient gas within the above range is desirable because theproportion of inert gas included in the total gas flow rate can beeasily controlled, and preparing an atmosphere containing inert gas thataccounts for at least 40 vol % of the total gas flow rate is easy.

By setting the proportion of inert gas in the total gas flow rate to atleast 40 vol %, in crystal growth on the principal plane of theunderlying substrate, decomposition of the underlying substrate surfaceduring growth (initial stage of growth) and of the crystal growthsurface (during thick-film growth) is reduced and feedstock wettabilityof the underlying substrate surface increases, making it possible toachieve two-dimensional growth that is capable of high-quality crystalgrowth. Stacking faults typically expand as the grown film thicknessincreases, but if two-dimensional growth or step-flow growth is carriedout at the initial stage of the growth step, stacking faults do notreadily expand in the periodic table Group 13 metal nitride layer thatis grown, making it easy to maintain a high-quality state even at alarger film thickness.

The proportion of inert gas may remain fixed during growth or may bevaried during growth, so long as it remains within the above range. Theperiod of time to change the content of the inert gases is preferably 1second or longer, more preferably 1 minute or longer and furtherpreferably 1 hour or longer. Such changes may entail changing all thetypes of gas at the same time, or changing each type of gas insuccession. Also, in the course of growth, the types of gas may be keptthe same without changing, or may be changed. For example, in oneconceivable case, N₂ is used as the inert gas at the initial stage ofgrowth, and argon is used as the inert gas during the main stage ofgrowth.

With a rise in the proportion of inert gas in the total gas flow rate,changes occur in the gas flow at the reactor interior. When the balancein gas flow from the respective inlets breaks down, a large amount ofpolycrystal adheres to the nozzle interior, leading to the problem ofreactor deterioration during cooling. Hence, a search was done for gasconditions that avoid the formation of polycrystal at the interior ofinlets when the periodic table Group 13 source and the nitrogen sourceare supplied as gases, whereupon it was found to be desirable for theratio of the density of a periodic table Group 13 source-containing gas(referred to below as “periodic table Group 13 source gas”) to thedensity of a nitrogen source-containing gas (referred to below as“nitrogen source gas”), which ratio is expressed as (periodic tableGroup 13 source gas density/nitrogen source gas density), to fall withina specific range. The periodic table Group 13 source gasdensity/nitrogen source gas density ratio is preferably less than 1, andmore preferably 0.8 or less. In this range, natural convection does notreadily arise between the inlet openings and the susceptor and theunderlying substrate surface, enabling the formation of polycrystalwithin the inlets to be suppressed, which is desirable. Here, theperiodic table Group 13 source gas and the nitrogen source gas are eachpresumed to be mixed gases of the source gas with carrier gas. Thedensity of the mixed gas can be calculated from the densities of therespective individual gases and the mixing ratio. The density can becalculated using, for example, formula (1) below.DT=Σ(DnLn)/ΣLn  (1)where DT: Density of mixed gas

Dn: Individual densities of respective gases

Ln: Feed rates of respective gases

3) Susceptor Material and Shape, and Distance of Susceptor from GrowthFace

The material making up the susceptor 107 is preferably carbon, and it ismore preferable for the surface to be coated with SiC. The shape of thesusceptor 107 is not particularly limited, provided it is a shape thatenables the base substrate used in the present invention to be placedthereon. However, it is preferable for there to be no structure presentnear the crystal growth face during crystal growth. Where a structurehaving a possibility to grow is present in the vicinity of a crystalgrow face, a polycrystal is adhered thereto, and HCl gas is generated asits product, and adversely affects a crystal to be grown. Contact facebetween the seed crystal 109 and the susceptor 107 separates from theprincipal plane (crystal growth face) of the seed crystal with adistance of preferably 1 mm or more, more preferably 3 mm or more andfurther preferably 5 mm or more.

4) Reservoir

The starting material for the periodic table Group 13 metal nitridesemiconductor to be grown is charged into the reservoir 105.Specifically, a starting material that may become a periodic table Group13 source is charged. Examples of such materials that may become aperiodic table Group 13 source include gallium (Ga), aluminum (Al) andindium (In). A gas that reacts with the starting material charged intothe reservoir 105 is fed in through an inlet 103 for introducing gasinto the reservoir 105. For example, when a starting material serving asthe periodic table Group 13 source has been charged into the reservoir105, HCl gas may be supplied via the inlet 103. At this time, a carriergas may be supplied via the inlet 103 together with the HCl gas. Thecarrier gas can include a gas such as hydrogen, nitrogen, He, Ne or Ar,and nitrogen is preferably used to produce a crystal which satisfiesQx_(1/300) of the present invention. Those gases may be used singly oras mixtures thereof.

5) Nitrogen Source (Ammonia), Separation Gas, Dopant Gas

A source gas becoming a nitrogen source is fed from an introduction tube104. NH₃ is generally fed. A carrier gas is fed from an introductiontube 101 and an introduction tube 102. The carrier gas can beexemplified by the same gases as the carrier gases fed from theintroduction tube 103. The carrier gas has the effect of suppressingreaction between source gases in the vapor phase and preventing adhesionof a polycrystal to the tip of the nozzles. A dopant gas can be fed fromthe introduction tube 102. For example, an n-type dopant gas such asSiH₄, SiH₂Cl₂ or H₂S can be fed.

6) Method of Introducing the Gases

The gases fed from the introduction tubes 101 to 104 may be fed fromdifferent introduction tubes from those described above by exchangingthe respective gases with each other. The source gas becoming a nitrogensource, and the carrier gas may be mixed and fed from the sameintroduction tube. Furthermore, the carrier gas may be mixed fromanother introduction tube. Those feed embodiments can appropriately bedetermined depending on the size and shape of the reactor 100,reactivity of raw materials, the desired crystal growth rate, and thelike.

7) Placement of Exhaust Tube

A gas exhaust tube 108 can be provided at the top, the bottom and theside of an inner wall of the reactor. The gas exhaust tube 108 ispreferably provided at a position lower than the crystal growth end fromthe standpoint of dust drop, and is more preferably provided at thebottom of the reaction as shown in FIG. 1.

8) Crystal Growing Conditions

Crystal growth in the manufacturing method of the invention is generallycarried out at 800° C. to 1200° C., preferably at 900° C. to 1100° C.,and more preferably at 950° C. to 1050° C. Exemplary conditions forproducing crystals which satisfy Qx_(1/300) in this invention include inparticular suppressing island growth and enhancing feedstock wettabilityat the surface of the underlying substrate so as to promotetwo-dimensional growth. From this standpoint, at the initial stage ofcrystal growth (0 to 15 minutes) and/or during the main stage of crystalgrowth, it is desirable for the growth temperature to be set to arelatively low temperature of preferably from 900° C. to 1000° C., andmore preferably from 920° C. to 980° C.

The crystal growth time is not particularly limited, and is generallyfrom 10 hours to 100 hours. The growth time may be suitably variedaccording to the target thickness to which the film is to be grown.Pressure in the reactor is preferably from 10 kPa to 200 kPa, morepreferably from 30 kPa to 150 kPa and further preferably from 50 kPa to120 kPa.

When introducing gases into the system at the start of crystal growth,setting the time required until each gas reaches the predetermined gaspartial pressure (gas flow rate), which time is referred to below as the“gas introduction time,” to a relatively short time influences thesurface morphology and growth regime of the initial growth layer. Thisis desirable because, even in cases where the periodic table Group 13metal nitride layer is subsequently rendered into a thick film, theoccurrence of anisotropic strain between the growth direction and thegrowth plane is suppressed, enabling the expansion and propagation ofstacking faults to be suppressed. The use of hydrogen gas-containingcarrier gas in the growth step is particularly desirable because theabove effects are easily obtained.

The partial pressure of gallium chloride (GaCl) is generally from 3×10¹to 3×10⁴ Pa, preferably from 4×10¹ to 2×10³ Pa, and more preferably from2×10² to 2×10³ Pa. The partial pressure of ammonia (NH₃) is generallyfrom 1×10³ to 3×10⁵ Pa, preferably from 2×10³ to 2×10⁴ Pa, and morepreferably from 4×10³ to 1×10⁴ Pa.

Also, it is preferable to carry out treatment which increases thepartial pressure of each type of gas for a predetermined period of timeat the initial stage of crystal growth. Increasing the partial pressureof each type of gas at the initial stage of crystal growth exerts aninfluence on the surface morphology and growth regime of the initialgrowth layer, resulting in a tendency for the occurrence of crystalstrain in subsequent bulk crystal formation to be suppressed and for theformation of stacking faults to be suppressed. In particular, such gaspartial pressure increasing treatment can be advantageously used as acondition for producing the bulk crystal from which regions that form ontop of regions formed by lateral growth are to be collected. Also, incases where H₂ carrier gas is used as the carrier gas, the occurrence ofstacking faults tends to be more effectively suppressed.

The amount of GaCl gas at the initial stage of crystal growth isgenerally at least 1.20×10² Pa, preferably at least 1.60×10² Pa, andmore preferably at least 2.00×10² Pa. The amount of GaCl gas at theinitial stage of crystal growth is generally not more than 9.00×10² Pa,preferably not more than 7.00×10² Pa, and more preferably not more than5.00×10² Pa.

The amount of H₂ carrier gas at the initial stage of crystal growth isgenerally at least 1.00×10³ Pa, preferably at least 5.00×10³ Pa, andmore preferably at least 1.00×10⁴ Pa. The amount of H₂ carrier gas atthe initial stage of crystal growth is generally not more than 7.00×10⁴Pa, preferably not more than 6.00×10⁴ Pa, and more preferably not morethan 5.00×10⁴ Pa.

The amount of HCl gas at the initial stage of crystal growth isgenerally at least 1.80×10¹ Pa, preferably at least 3.00×10¹ Pa, andmore preferably at least 4.00×10¹ Pa. The amount of HCl gas at theinitial stage of crystal growth is generally not more than 2.00×10² Pa,preferably not more than 1.50×10² Pa, and more preferably not more than1.00×10² Pa.

The introduction time of each of these gases is generally preferably 10minutes or less, more preferably 5 minutes or less, even more preferably2 minutes or less. Further, the gas introduction time is usually 10seconds or more, preferably 20 seconds or more, and more preferably 30seconds or more. By setting the gas introduction time in the aboverange, surface roughness of the underlying substrate at the initialstage of the growth step decreases and island growth can be effectivelysuppressed. Also, it is presumed that by reaching the desired gasconditions in a short time, the occurrence of stacking faults anddislocations can be suppressed.

The H₂ carrier gas partial pressure during temperature ramp-up up untilreaching the crystal growth conditions is generally at least 1.00×10²Pa, preferably at least 3.00×10² Pa, and more preferably at least5.00×10² Pa. The H₂ carrier gas partial pressure during temperatureramp-up until reaching the crystal growth conditions is generally notmore than 5.00×10⁴ Pa, preferably not more than 4.00×10⁴ Pa, and morepreferably not more than 3.00×10⁴ Pa.

The N₂ carrier gas partial pressure during temperature ramp-up isgenerally not more than 9.00×10⁴ Pa.

The NH₃ partial pressure during temperature ramp-up is generally atleast 3.00×10³ Pa, preferably at least 5.00×10³ Pa, and more preferablyat least 7.00×10³ Pa. The NH₃ partial pressure during temperatureramp-up up until reaching the crystal growth conditions is generally notmore than 6.00×10⁴ Pa, preferably not more than 4.00×10⁴ Pa, and morepreferably not more than 2.00×10⁴ Pa.

9) Crystal Growth Rate

The rate of crystal growth using the above-described productionequipment varies depending on such factors as the growth process, thegrowth temperature, the feed rate of the source gases and the directionof the crystal growth face, but is generally in the range of from 5 μm/hto 500 μm/h, preferably 30 μm/h or more, more preferably 70 μm/h ormore, and even more preferably 150 μm/h or more. The growth rate can becontrolled by appropriately setting the kind and flow rate of carriergas, the distance from feed opening to crystal growth end, and the like,in addition to those described above. For example, by making the flowrate of the gallium chloride (GaCl) serving as the periodic table Group13 metal source and/or the flow rate of the ammonia (NH₃) serving as thenitrogen source larger and thus making the partial pressures of thesegases higher, the growth rate can be increased.

Examples of Group 13 metal nitride crystals in the periodic table of thepresent invention include gallium nitride, aluminum nitride, indiumnitride, and mixed crystals thereof.

The periodic table Group 13 metal nitride crystal of the invention has acarrier concentration in the crystal of preferably at least 1×10¹⁸ cm⁻³,and more preferably at least 1×10¹⁹ cm⁻³. When the carrier concentrationin the crystal is high, the resistivity within the crystal is low,giving a semiconductor crystal having excellent electrical conductivity.The carrier concentration within the crystal can be determined bymeasuring the Hall coefficient using the van der Pauw method.

The Group 13 metal nitride crystals in the periodic table of the presentinvention can be used in various applications. In particular, thenitride crystal is useful as substrates of light emitting elements atrelatively short wavelength side, such as ultraviolet, blue or greenlight emitting diodes and semiconductor lasers, and semiconductordevices such as electronic devices.

<Periodic Table Group 13 Metal Nitride Crystal Substrate>

1) Characteristics

A periodic table Group 13 metal nitride crystal substrate can beobtained by removing at least a portion of the underlying substrate fromthe periodic table Group 13 metal nitride crystal of the invention. Theperiodic table Group 13 metal nitride crystal substrate is characterizedin that a non-polar plane or a semi-polar plane preferably serves as aprincipal plane, that warpage of the substrate in the direction of theline of intersection between a polar plane and the principal plane issmaller than warpage of the substrate in a direction orthogonal to thisline of intersection, and that warpage of the substrate in a directionorthogonal to the line of the intersection is less than 1° per 40 mm.The direction of this line of intersection and the direction orthogonalthereto are both directions assumed to be within the plane of thesubstrate.

2) Thickness

The periodic table Group 13 metal nitride crystal substrate obtainedfrom the periodic table Group 13 metal nitride crystal of the inventionis preferably a self-supporting substrate. Specifically, the thicknessis preferably 0.2 mm or more, more preferably 0.3 mm or more and evenmore preferably 0.4 mm or more. The substrate thickness and size can beadjusted within the desired ranges by the suitable regulation ofpolishing, cutting, etching and the like.

3) Principal Plane

The principal plane of the periodic table Group 13 metal nitride crystalsubstrate obtained from the periodic table Group 13 metal nitridecrystal of the invention may be either a non-polar plane or a semi-polarplane, although it is preferably a low-index plane. For example, in acase where the base substrate is a hexagonal crystal whose principalplane is represented by (hklm), h, k, l and m are each independently anyinteger which is preferably from −3 to 3, and more preferably from −2 to2. Illustrative examples of the principal plane of the periodic tableGroup 13 metal nitride crystal substrate include {20-21} planes,{20-2-1} planes, {30-31} planes, {30-3-1} planes, {10-11} planes,{10-1-1} planes, {10-12} planes, {10-1-2} planes, {11-22} planes,{11-2-2} planes, {11-21} planes, and {11-2-1} planes. Of these, {20-21}planes, {20-2-1} planes, {30-31} planes, {30-3-1} planes, {10-11} planesand {10-1-1} planes are preferred.

The warpage of the substrate in the direction orthogonal to the line ofintersection of the periodic table Group 13 metal nitride crystalsubstrate obtained by the Group 13 metal nitride crystals in theperiodic table of the present invention is preferably less than 1° per40 mm, more preferably less than 0.80°, even more preferably less than0.60°, and particularly preferably less than 0.40°. The substratewarpage in the direction of the line of intersection is preferably lessthan 0.85° per 40 mm, more preferably less than 0.65°, even morepreferably less than 0.45°, and particularly preferably less than 0.25°.The difference between the substrate warpage per 40 mm in the directionorthogonal to the line of intersection and the substrate warpage per 40mm in the direction of the line of intersection is generally from 0.02to 1.0°, preferably from 0.03 to 0.75°, and more preferably from 0.05 to0.5°.

For example, in cases where the principal plane of the periodic tableGroup 13 metal nitride crystal substrate is a {10-10} plane (i.e., an Mplane) of a hexagonal crystal, the warpage in the direction of the lineof intersection (i.e., the a-axis direction) between the {0001} planewhich is a polar plane (i.e., a C plane) and the principal plane issmaller than the warpage in the direction orthogonal thereto (i.e., thec-axis direction). The c-axis direction warpage in this case is lessthan 1° per 40 mm. In another example, when the principal plane of aperiodic table Group 13 metal nitride crystal substrate is the (11-20)plane (i.e., the A plane) of a hexagonal crystal, the warpage in thedirection of the line of intersection (i.e., the m-axis direction)between the (0001) plane which is a polar plane (i.e., a C plane) andthe principal plane is smaller than the warpage in the directionorthogonal thereto (i.e., the c-axis direction). The c-axis directionwarpage in this case is less than 1° per 40 mm.

The ratio (W1/W2) between the warpage of the substrate in the directionof the line of intersection between the polar plane and the principalplane (W1), and the warpage of the substrate in the direction orthogonalto the line of intersection (W2) is preferably less than 1, morepreferably less than 0.8, and even more preferably less than 0.5.Further, the lower limit value is preferably 0.01 or more, morepreferably 0.02 or more, and even more preferably 0.04 or more.

(4) Crystallinity of Substrate and Crystal Formed on Substrate

When a periodic table Group 13 metal nitride crystal is homoepitaxiallygrown on the principal plane of a periodic table Group 13 metal nitridecrystal substrate obtained from the periodic table Group 13 metalnitride crystal of the invention, most of the stacking faults that formwithin the grown crystal are parallel to a polar plane. The stackingfaults can be identified by observation in cathodoluminescence (CL)measurement of the crystal surface at a low temperature, as describedbelow in the working examples.

For example, in a periodic table Group 13 metal nitride crystalsubstrate having the (10-10) plane (i.e., an M plane) as the principalplane, when a periodic table Group 13 metal nitride crystal is grown onthe principal plane, it is primarily stacking faults parallel to the(0001) plane which is a polar plane (i.e., a C plane) that arise. Uponexamination from the principal plane side in low-temperature CLmeasurement, stacking faults in the form of straight lines which extendin the a-axis direction are observed.

The periodic table Group 13 metal nitride crystal substrate obtainedfrom the periodic table Group 13 metal nitride crystal of the inventionand the crystal formed on this substrate contain few stacking faults,and thus exhibit good luminescence when used as semiconductorlight-emitting devices such as LEDs. The degree of stacked faults is thesame as for periodic table Group 13 metal nitride layer obtained by theabove-described manufacturing method of the invention.

Threading dislocations are present in the principal plane of theperiodic table Group 13 metal nitride crystal substrate and the crystalformed on this substrate. This is due to the fact that, becausethreading dislocations generally form in such a way as to extend in thegrowth direction of the crystal, threading dislocations are present inthe growth plane of a crystal grown on an underlying substrate, ascalled for in the manufacturing method of the invention. The threadingdislocations generally coincide with the dark points observed in CLmeasurement.

<Semiconductor Light-Emitting Device>

Semiconductor light-emitting devices can be fabricated using theperiodic table Group 13 metal nitride crystal substrate obtained fromthe periodic table Group 13 metal nitride crystal of the invention.Generally, the semiconductor light-emitting device, such as an LED, isproduced by growing Group 13 metal nitride crystals in the periodictable on the principal plane of the periodic table Group 13 metalnitride crystal substrate. Illustrative examples of the Group 13 metalnitride crystals in the periodic table that are grown include GaN,GaAlAs, AlInGaP, and InGaN. The crystal growth method is exemplified by,but not particularly limited to, metal organic chemical vapor deposition(MOCVD). By growing a crystal on a periodic table Group 13 metal nitridecrystal substrate, the number of crystal defects is lower than when thecrystal is grown on a conventional sapphire base substrate or on aperiodic table Group 13 metal nitride crystal substrate having manystacking faults. Hence, high-power, durable semiconductor light-emittingdevices can be provided.

EXAMPLES

The features of the present invention are illustrated more concretelybelow by way of working examples of the invention and comparativeexamples. The materials, usage amounts, ratios, treatment details, orderof treatment and the like shown in the following examples can besuitably varied without departing from the gist of the invention.Therefore, the scope of the present invention should not limitedly beconstrued by the following specific examples.

Example 1 N₂ Carrier Growth

Crystal growth was carried out using the HVPE crystal manufacturingapparatus shown in FIG. 1. A single GaN self-supporting substrate 1which was produced by (0001) plane growth, was of rectangular shapemeasuring 5 mm in the <0001> (c-axis) direction and 25 mm in the <11-20>(a-axis direction), and had a principal plane that was the (10-10) planeand was tilted 2° in the [000-1] direction was placed on a susceptor107. The susceptor 107 with the substrate loaded thereon was placed in areactor 100 as shown in FIG. 1. Next, the interior of the reactor wasflushed with N₂ gas, following which the periodic table Group 13 sourcereservoir temperature was raised to 900° C. and the reaction chambertemperature was raised to 950° C. so that gas convection does not arisewithin the reactor in the above atmosphere, and a GaN single-crystalfilm was grown for 15 hours by HVPE. In this single-crystal growth step,the growth pressure was set to 1.01×10⁵ Pa, the partial pressure of GaClgas was set to 2.85×10² Pa, the partial pressure of NH₃ gas was set to9.13×10³ Pa, and the partial pressure of N₂ gas serving as a carrier gaswas set to 9.19×10⁴ Pa. Following completion of the single-crystalgrowth step, the temperature was lowered to room temperature and a GaNbulk crystal 1 was obtained. The crystal had an average grown filmthickness of 1.1 mm in the [10-10] direction.

The resulting GaN bulk crystal 1 was shaped and subjected to surfacepolishing treatment, after which surface grinding was conducted theretoby the customary technique, then polishing was subsequently carried out,thereby producing a 330 μm thick free-standing rectangular GaN substrate2 having a length of 4 mm in the direction of <0001> (c-axis) and alength of 20 mm in the direction of <11-20> (a-axis), in which theprincipal plane was (10-10) plane. The stacking fault density of the GaNcrystal produced was determined by low-temperature photoluminescence(PL) measurement (LTPL measurement). A He—Cd laser having a centerwavelength of 325 nm as the excitation light source was used at ameasurement temperature of 10 K. The intensity ratio I(BSF)/I(D⁰X_(A))of the 3.41 eV peak intensity from stacking faults (BSF) to the 3.47 eVpeak intensity I(D⁰X_(A)) from band-edge luminescence had a good valueof 0.0045.

X-rays were made to enter the (100) plane of the resulting GaNself-supporting substrate 2 in a direction perpendicular to the a-axisand reciprocal lattice mapping measurement of the (100) plane wascarried out. In the Qx direction profile that includes a maximumintensity and is derived from an isointensity contour plot obtained bysuch mapping, the width at the foot of the peak (Qx width) wasestimated.

Measurement was carried out with a high-resolution x-ray diffractometer(X'Pert Pro MRD, available from PANalytical B.V.).

The x-ray beam was generated using a line focus x-ray tube, with adivergence slit inserted before a Ge (220) asymmetrical two-reflectionmonochromator, using the CuKα1 line, with a pinhole collimator mountedin front of the monochromator, and such as to have the full width athalf maximum (FWHM) of Gaussian function approximations at the surfaceof the GaN self-supporting substrate 2 be 100 μm in the horizontaldirection and 400 μm in the vertical direction. The beam was parallel tothe direction perpendicular to the ω axis of rotation, and the beamdiameter in the horizontal direction orthogonal thereto was sufficientlynarrowed to 100 μm, making it possible to eliminate the influence ofcrystal plane curvature (warpage) on the diffracted beam.

A one-dimensional semiconductor detector having a high angularresolution was used as the detector.

The incident direction of the x-ray beam was set by carrying out aso-called Phi scan in such a way that the diffraction intensity of theasymmetric (20-4) plane becomes a maximum, deciding on the sampledirection, and having the incident direction be exactly perpendicular tothe a-axis.

The sample was axially aligned in the (100) diffraction plane, afterwhich a 2θ−ω two-axis scan was carried out in angular steps of 0.005°for both 2θ and ω over a measurement angle range of 1°. The resulting2θ−ω two-dimensional intensity mapping data was converted to Qx-Qycoordinate system data, thereby giving reciprocal lattice map data. In aQx direction profile that includes a maximum intensity and is derivedfrom an isointensity contour plot obtained from this data, the width atthe foot of the peak (Qx width) was estimated.

The Qx widths at 1/300th and 1/1000th of the peak intensity wererespectively 1.77×10⁻⁴ (rlu) and 2.55×10⁻⁴ (rlu), which were very smallvalues.

Next, the anisotropy of the x-ray rocking curve was measured.

As with reciprocal lattice mapping measurement, measurement here too wascarried out using a high-resolution x-ray diffractometer (X'Pert ProMRD, from PANalytical B.V.)

The x-ray beam was generated using a line focus x-ray tube, with adivergence slit inserted before a Ge (220) asymmetrical two-reflectionmonochromator, using the CuKα1 line, with a pinhole collimator mountedin front of the monochromator, and such as to have the full width athalf maximum (FWHM) of Gaussian function approximations at the sample be100 μm in the horizontal direction and 400 μm in the vertical direction.In this example, during rocking curve measurement (ω scan), aone-dimensional array-type semiconductor detector was used, although acommonly used proportional counting-type detector may be employed.

As in the reciprocal lattice mapping measurement described above, thex-ray beam was made to enter from a direction perpendicular to thea-axis, and the (100) rocking curve was measured with a one-dimensionalarray-type semiconductor detector in open detector mode. The full widthat half maximum of the peak intensity and the spectral widths at 1/300thand 1/1000th of the peak intensity were respectively 25.5 arc-sec, 184arc-sec and 335 arc-sec.

Next, the GaN self-supporting plate 2 was rotated 90°, the x-ray beamwas made to enter from a direction perpendicular to the c-axis, and therocking curve of the (100) plane (Open detector) was measured. The fullwidth at half maximum of the peak intensity and the spectral widths at1/300th and 1/1000th of the peak intensity were respectively 26.0arc-sec, 164 arc-sec and 292 arc-sec.

The spectral widths of (100) XRC when the x-ray beam enters from adirection perpendicular to the a-axis were divided by the spectralwidths of (100) XRC when the x-ray beam enters from a directionperpendicular to the c-axis, and the resulting ratios were calculated.These ratios for the full width at half maximum of the peak intensityand for the spectral widths at 1/300th and 1/1000th of the peakintensity were respectively 0.98, 1.12 and 1.15, indicating that theanisotropy was small. By thus adopting the spectral width ratios asindicators of the crystal characteristics, it is possible to extractdata that is not easily influenced by the optical system used duringx-ray diffraction measurement.

The misorientation angle distribution in the c-axis direction of the GaNself-supporting substrate 2 was found to be, for a distance of 40 mm,±0.12°, which is a very small value. The measurement range was set to 15mm and the measurement interval was set to 1 mm.

Also, an undoped GaN layer was grown to 1 μm by MOCVD on a GaNself-supporting substrate 2, and the stacking fault density wasevaluated by cathodoluminescence (CL) measurement.

Using a SEM-CL system, cathodoluminescence (CL) image at about 100 K wasexamined in substantially the same region as the place where x-raydiffraction measurement of the GaN self-supporting substrate 2 wascarried out, and the basal plane stacking fault (BSF) density wasmeasured. The electron beam used in scanning electron microscopy had anacceleration voltage of 5 kV. Aside from the residual donor-boundexciton emission peak (approx. 356 nm) from spectrum measurement, a weakemission peak from BSF (approx. 364 nm) was observed. The spectrometerwas set to 364 nm, and the spatial distribution of BSFs was observed.BSFs extending in a direction perpendicular to the c-axis of the samplewere seen; the average length of a-axis direction BSFs observed on them-plane surface was 33 μm. To estimate the stacking fault density perunit length, the number of BSFs within the field of view of the CL imageobserved was determined at a sampling interval (20 μm) shorter than theaverage length of the BSFs observed at the surface, and the averagevalue was calculated, giving a very small value of 6×10/cm.

Example 2 N₂ Carrier Growth

Crystal growth was carried out using the HVPE crystal manufacturingapparatus shown in FIG. 1. A GaN self-supporting substrate which wasmanufactured by (0001) plane growth, was of rectangular shape measuring5 mm in the <0001> (c-axis) direction and 25 mm in the <11-20> (a-axisdirection), and had a principal plane tilted 1° in the [000-1] directionfrom the (10-10) plane was placed as the underlying substrate on asusceptor 107. The susceptor 107 on which the underlying substrate hadbeen placed was situated as shown in FIG. 1 in the reactor 100. Next,the reactor interior was flushed with N₂ gas, following which, in thisatmosphere, the temperature of the periodic table Group 13 sourcereservoir 106 was raised to 900° C., the reaction chamber temperaturewas raised to 950° C., and a GaN single-crystal layer was grown for 15hours by HVPE. In this single-crystal growth step, the growth pressurewas set to 1.01×10⁵ Pa, the partial pressure of GaCl gas was set to2.85×10² Pa, the partial pressure of NH₃ gas was set to 9.13×10³ Pa, andthe percentage of inert gas (N₂) in the total gas flow rate was set to91 volume %. The periodic table Group 13 source gas density/nitrogensource gas density at this time was set to 1.09, and the gasintroduction time was set at 1 minute.

Following completion of the single-crystal growth step, the temperaturewas lowered to room temperature and a GaN bulk crystal was obtained. Thecrystal grown on the underlying substrate had an average grown filmthickness of about 1 mm in the [10-10] direction. Some polycrystal wasattached to the inlets. The results are shown in Table 1.

Examples 3 to 7

In each of these examples, aside from changing the misorientation angleof the principal plane in the [000-1] direction and the growthtemperature to the conditions indicated in Table 1, a GaN bulk crystalwas obtained in the same way as in Example 2. The crystal grown on theunderlying substrate had an average film thickness in the [10-10]direction of about 1 mm. The results are presented in Table 1.

TABLE 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7Underlying Underlying substrate GaN GaN GaN GaN GaN GaN substrateOrientation of principal plane (10-10) (10-10) (10-10) (10-10) (10-10)(10-10) Misorientation angle of principal 1 2 3 5 1 2 Plane in -c-axisdirection (°) GaN layer Growth temperature (° C.) 950 950 950 950 10001000 Growth rate (μm/hr) 76 75 75 77 69 68 LTPL intensity ratio(I(BSF)/I(D⁰X_(A)) 0.08 0.03 0.04 0.08 0.11 0.04 Presence/absence ofcracks No cracks No cracks No cracks No cracks No cracks No cracks

The stacking fault densities of the GaN bulk crystals obtained wereevaluated by low-temperature photoluminescence measurement (LTPLmeasurement). A He—Cd laser having a center wavelength of 325 nm as theexcitation light source was used at a measurement temperature of 10 K.The ratios of the peak intensity I(BSF) at 3.41 eV from stacking faultsto the peak intensity I(D⁰X_(A)) at 3.47 eV from band-edge luminescence(which ratios are referred to here as I(BSF)/I(D⁰X_(A))) in samplesgrown at a growth temperature of 950° C. and using an underlyingsubstrate in which the principal plane had a misorientation angle in the[000-1] direction of 2° or 3°, were 0.03 and 0.04, which are smallvalues. These results suggest that the stacking fault density is small.

Furthermore, the sample of Example 3 was shaped and subjected to surfacepolishing treatment, after which surface grinding was conducted theretoby the customary technique, then polishing was subsequently carried out,thereby producing a 330 μm thick free-standing rectangular GaN substratehaving a length of 4 mm in the direction of <0001> (c-axis) and a lengthof 20 mm in the direction of <11-20> (a-axis), in which the principalplane was (10-10) plane. An undoped GaN layer was grown to 1 μm on thissubstrate using a MOVPE system, and the stacking fault density wasdetermined by low-temperature cathodoluminescence (LTCL) observation at4 kV and 500 pA in a 200× field of view. In the LTCL image, thehorizontal lines present in directions parallel to the C plane arestacking faults. The stacking fault density was calculated in this way,giving a good value of 5.28×10² cm⁻¹. These results confirmed theadvantage of using N₂ as the carrier gas and using as the substrate anunderlying substrate with a principal plane having a misorientationangle in the [000-1] direction of 2°.

Reference Example

Growth of a periodic table Group 13 nitride layer was carried out forjust 1 minute under the same conditions as in Example 2, and the surfaceof the periodic table Group 13 nitride layer obtained by completinggrowth after 1 minute was examined with a scanning electron microscope.The results are shown in FIG. 3A. At the surface of this sample, aperiodic table Group 13 nitride layer had formed uniformly over theentire surface of the underlying substrate, and it was apparent thattwo-dimensional growth had occurred. This implied that, in theabove-described working examples as well, the mode of growth at theinitial stage of the growth step was two-dimensional growth.

Comparative Example 1

Crystal growth was carried out using the HVPE crystal manufacturingapparatus shown in FIG. 1. A GaN self-supporting substrate which wasmanufactured by (0001) plane growth, was of rectangular shape measuring5 mm in the <0001> (c-axis) direction and 25 mm in the <11-20> (a-axisdirection), and had a principal plane that was tilted 1° in the [000-1]direction from the (10-10) plane was placed on a susceptor 107. Thesusceptor 107 with the substrate loaded thereon was placed in a reactor100 as shown in FIG. 1. Next, the reactor interior was flushed with N₂gas, following which the periodic table Group 13 source reservoirtemperature 106 was raised to 900° C. and the reaction chambertemperature was raised to the growth temperature of 1040° C. in theabove atmosphere, and a GaN single-crystal layer was grown for 15 hoursby HVPE. In this single-crystal growth step, the growth pressure was setto 1.01×10⁵ Pa, the partial pressure of GaCl gas was set to 3.26×10² Pa,the partial pressure of NH₃ gas was set to 1.04×10⁴ Pa, and thepercentage of inert gas (N₂) in the total gas flow rate was set to 12volume %. The periodic table Group 13 source gas density/nitrogen sourcegas density ratio at this time was set to 0.83, and the gas introductiontime was set to 1 minute.

Following completion of the single-crystal growth step, the temperaturewas lowered to room temperature and a GaN bulk crystal was obtained. Thecrystal grown on the underlying substrate had an average film thicknessof about 1 mm in the [10-10] direction. Moreover, no polycrystaladhesion whatsoever was found in the inlets.

The stacking fault density of the GaN bulk crystal obtained wasevaluated by low-temperature photoluminescence measurement (LTPLmeasurement). A He—Cd laser having a center wavelength of 325 nm as theexcitation light source was used at a measurement temperature of 10 K.The intensity ratio I(BSF)/I (D⁰X_(A)) of the peak intensity I(BSF) at3.41 eV from stacking faults to the peak intensity I(D⁰X_(A)) at 3.47 eVfrom band-edge luminescence was 0.63. Compared with the results fromExamples 2 to 7, the stacking fault density at places having a grownfilm thickness of about 1 mm was poor.

Reference Comparative Example

Growth of a periodic table Group 13 nitride layer was carried out forjust 1 minute under the same conditions as in Comparative Example 1, andthe surface of the periodic table Group 13 nitride layer obtained bycompleting growth after 1 minute was examined with a scanning electronmicroscope. The results are shown in FIG. 3B. At the surface of thissample, a periodic table Group 13 nitride layer formed as islands andmany regions were seen where the underlying substrate is exposed. It wasapparent that growth of the periodic table Group 13 nitride layer wasnon-uniform and that two-dimensional growth had not occurred. Thisimplied that, in the above Comparative Example 1 as well, the mode ofgrowth at the initial stage of the growth step was three-dimensionalgrowth rather than two-dimensional growth.

Example 8

Crystal growth was carried out using a HVPE crystal manufacturingapparatus. A total of 22 GaN self-supporting substrates weremanufactured by (0001) plane growth. Each was of a rectangular shapemeasuring 5 mm in the <0001> (c-axis) direction and 30 mm in the <11-20>(a-axis direction), and had a principal plane that was tilted 2° in the[000-1] direction from the (10-10) plane. The 22 substrates werearranged in two rows in the <0001> (c-axis) direction and 11 rows in the<11-20> (a-axis) direction, and placed on a susceptor. The susceptor onwhich the arranged substrates had been mounted was placed in thereactor, the temperature of the periodic table Group 13 source reservoir106 was raised to 900° C. and the temperature of the reaction chamberwas raised to the growth temperature of 950° C., and a GaNsingle-crystal layer was grown by HVPE for 53 hours. In thissingle-crystal growth step, the growth pressure was set to 1.01×10⁵ Pa,the partial pressure of GaCl gas was set to 3.54×10² Pa, the partialpressure of NH3 gas was set to 1.13×10⁴ Pa, and the percentage of inertgas (N₂) in the total gas flow rate was set to 49 volume %. The periodictable Group 13 source gas density/nitrogen source gas density ratio atthis time was 0.72, and the gas introduction time was 1 minute.

Following completion of the single-crystal growth step, the temperaturewas lowered to room temperature and a GaN bulk crystal was obtained. Thecrystal had an average film thickness of 2.2 mm in the [10-10]direction. Moreover, no polycrystal adhesion whatsoever was found in theinlets.

The dislocation density of the resulting GaN bulk crystal was evaluatedin the as-grown state by cathodoluminescence (CL) microscopy at 3 kV,500 pA and in a 500× field of view. In CL microscopy, the number ofthreading dislocations within the crystal was computed from the darkpoint density, giving a good value of 9.0×10⁵ cm⁻².

Evaluation of a stacking fault was conducted by carrying outlow-temperature photoluminescence (PL) measurement (LTPL measurement) byusing a He—Cd laser having a center wavelength of 325 nm as theexcitation light source at a measurement temperature of 10 K. Theintensity ratio I(BSF)/I(D⁰X_(A)) of the peak intensity I(BSF) at 3.41eV from stacking faults to the peak intensity I(D⁰X_(A)) at 3.47 eV fromband-edge luminescence was 0.09 in this sample, which is much smallerthan the value of 1.1 for the sample in Comparative Example 1 that wasgrowth at an inert gas ratio of 12 vol %, suggesting that the stackingfault density was low. From the above results, it was confirmed to beadvantageous to include in the overall gas flow rate at least 40 vol ofthe inert gas N₂.

The resulting GaN bulk crystal was shaped and subjected to surfacepolishing treatment, after which it was sliced by the customarytechnique, then polishing was subsequently carried out, therebyproducing two 330 μm thick free-standing circular GaN substrates withthe diameter of 50 mm, in which the principal plane was (10-10) plane.The rocking curve (Open detector) for the (100) plane when x-raysentered the GaN self-supporting substrate thus obtained from a directionperpendicular to the a-axis was measured at 5 points in the plane. Thespectral widths at one half of the peak intensity (FWHM) were very goodvalues of, respectively, 28 to 37 arc-sec and 23 to 45 arc-sec.

The samples were rotated 90° and the rocking curve (Open detector) forthe (100) plane when x-rays entered from a direction perpendicular tothe c-axis was measured at 5 points in the plane. The spectral widths atone half of the peak intensity (FWHM) were very good values of,respectively 24 to 51 arc-sec and 24 to 70 arc-sec.

Example 9 Crystal Growth Using Seed Crystal in which Substrate Sidewallis Semi-Polar Plane

(Production of Seed Crystal)

Crystal growth was carried out using the HVPE crystal manufacturingapparatus shown in FIG. 1. A total of 33 GaN self-supporting substrates1′ were manufactured by (0001) plane growth. Each was of a rectangularshape measuring 5 mm in the <0001> (c-axis) direction and 25 mm in the<11-20> (a-axis direction), and had a principal plane that was the(10-10) plane. The 33 substrates were arranged in three rows in the<0001> (c-axis) direction and 11 rows in the <11-20> (a-axis) direction,and placed on a susceptor 107. The susceptor 107 with the arrangedsubstrates loaded thereon was placed in a reactor 100 as shown in FIG.1, the temperature of the reaction chamber was raised to 1000° C., and aGaN single-crystal film was grown for 40 hours by the HVPE process. Inthis single-crystal growth step, the growth pressure was set to 1.01×10⁵Pa, the partial pressure of GaCl gas was set to 3.70×10² Pa, the partialpressure of NH₃ gas was set to 1.69×10³ Pa, the partial pressure of H₂carrier gas G1 was set to 6.00×10² Pa, and the partial pressure of N₂carrier gas was set to 8.29×10³ Pa. Following completion of thesingle-crystal growth step, the temperature was lowered to roomtemperature and a GaN bulk crystal 1′ was obtained. The crystal had anaverage grown film thickness of 2.8 mm in the [10-10] direction. Theresulting GaN bulk crystal 1′ was shaped and subjected to surfacepolishing treatment, after which it was sliced by the customarytechnique, then polishing was subsequently carried out, therebyproducing a 330 μm thick free-standing circular GaN substrate 2′ withthe diameter of 50 mm, in which the principal plane was (10-10) plane.

Dicing from the GaN self-supporting substrates 2′ produced as describedabove was carried out in such a way that a portion of the sidewallformed at the (11-24) plane (which coincides with the plane that formsan angle of 39° with the (0001) plane). In this way, rectangularcrystals measuring 3 mm in the <11-24> direction and 35 mm in the<11-20> (a-axis) direction and whose principal plane is the (10-10)plane were produced. Polishing was then carried out, producingrectangular GaN self-supporting substrates 3′ having a thickness of 330μm. By placing each end of the GaN self-supporting substrates 3′ on 1 cmsquare PG plates lying on a susceptor 107, the GaN self-supportingsubstrates 3′ were arranged so as to create a gap between the center ofthe substrate and the susceptor 107. A GaN single-crystal film was grownby HVPE for 40 hours.

In a mixed gas atmosphere in which the partial pressure of the H₂carrier gas was 6.00×10² Pa, the partial pressure of the N₂ carrier gaswas 8.29×10³ Pa and the partial pressure of the NH₃ gas was 1.13×10⁴ Pa,the temperature of the reaction chamber was raised to 1040° C. and heldfor 1 minute.

Growth of the GaN single-crystal film by HVPE was begun as describedbelow.

After holding the temperature for 1 minute as mentioned above, thepartial pressure of the GaCl gas was increased from 0 Pa to 3.54×10² Paand the partial pressure of HCl gas was increased from 0 Pa to 6.00×10¹Pa for 1 minute. The partial pressure of the H₂ carrier gas, after beingheld for 1 minute as mentioned above, was increased from 6.00×10² Pa to4.00×10⁴ Pa over 1 minute. In the subsequent single-crystal growth step,the growth pressure to the end of growth was set to 1.01×10⁵ Pa, thepartial pressure of the GaCl gas was set to 3.54×10² Pa, and the partialpressure of the NH₃ gas was set to 1.13×10⁴ Pa. Following completion ofthe single-crystal growth step, the temperature was lowered to roomtemperature and a GaN crystal was obtained.

No abnormal growth was observed in the resulting GaN single crystals,which were crack-free. The growth thickness was about 4.3 mm in them-axis direction (for the top and back faces combined) and about 7.0 mmin the [11-24] direction, Hence, in spite of the fact that the growthconditions were the same, differences in the growth rate depending onthe planar orientation were confirmed. The growth rate in the [11-24]direction was 175 μm/hr, and was thus confirmed to be at least 1.5 timesfaster than the growth rate in the principal plane direction.

In a wing growth region (a region that forms on top of lateral growth)of the resulting GaN crystal, an approximately 1.2 mm thick growthportion (a portion having a thickness of about 1.2 mm, in the directionin which the thickness of the overall crystal increases, from a boundaryplane between a region formed by lateral growth from the sidewall of theseed crystal and a region formed on top of lateral growth) was sliced ina principal plane having a misorientation angle of 5° in the <000-1>direction from the (10-10) plane. The GaN crystal was further polishedusing a diamond abrasive and surface polished by chemical mechanicalpolishing (CMP), thereby producing a 400 μm thick free-standing GaNsubstrate 4′ whose principal plane has an off-angle of 5° in thedirection of <000-1> from (10-10) plane.

The physical properties of a portion of the GaN self-supportingsubstrate 4′ thus produced and located about 2 mm away from the originalseed in the [11-24] direction were evaluated in the same way as inExample 1.

A reciprocal lattice map of the (100) plane when x-rays entered in adirection perpendicular to the a-axis was measured. In the Qx directionprofile that includes a maximum intensity and is derived from anisointensity contour plot obtained by such mapping, the width at thefoot of the peak (Qx width) was estimated.

The Qx widths at 1/300th and 1/1000th of the peak intensity wererespectively 3.6×10⁻⁴ (rlu) and 6.0×10⁻⁴ (rlu), which were very smallvalues.

As in the reciprocal lattice map measurement described above, the x-raybeam was made to enter from a direction perpendicular to the a-axis, andthe (100) rocking curve (Open detector) was measured. The full width athalf maximum of the peak intensity and the spectral widths at 1/300thand 1/1000th of the peak intensity were respectively 61.8 arc-sec, 338.4arc-sec and 612.0 arc-sec.

Next, the GaN self-supporting plate 4′ was rotated 90° about the m-axisas the center, the x-ray beam was made to enter from a directionperpendicular to the c-axis, and the (100) rocking curve (Open detector)was measured. The full width at half maximum of the peak intensity andthe spectral widths at 1/300th and 1/1000th of the peak intensity wererespectively 32.5 arc-sec, 194.4 arc-sec and 338.4 arc-sec.

The spectral width of (100) XRC when the x-ray beam entered from adirection perpendicular to the a-axis was divided by the spectral widthof (100) XRC when the x-ray beam entered from a direction perpendicularto the c-axis, and the ratio of these was calculated. The ratio for thefull width at half maximum of the peak intensity and the ratios for thespectral widths at 1/300th and 1/1000th of the peak intensity wererespectively 1.90, 1.74 and 1.81, indicating that the anisotropy wassmall.

Also, an undoped GaN layer was grown to 1 μm by MOCVD on a GaNself-supporting substrate 4′, and evaluation of the stacking faultdensity by cathodoluminescence (CL) measurement was carried out,yielding a result of 3×10²/cm. The stacking faults observed by CL at thesurface of the m-plane had lengths in the a-axis direction that were atleast 200 μm.

Example 10 Crystal Growth Using Seed Crystals in which SubstrateSidewall was a Semi-Polar Plane

Dicing from the GaN self-supporting substrates 2′ produced by themanufacturing method described in Example 9 was carried out in such away that a portion of the sidewall formed at the (11-24) plane (whichcoincides with the plane an angle of 39° with the (0001) plane). In thisway, rectangular crystals measuring 3 mm in the <11-24> direction and 35mm in the <11-20> (a-axis) direction and whose principal plane is the(10-10) plane were produced. Polishing was then carried out, producingrectangular GaN self-supporting substrates 3″ having a thickness of 330μm. Both ends of the GaN self-supporting substrates 3″ were placed on PGplates lying on a susceptor 107 at intervals corresponding to the lengthof the long sides of the self-supporting substrates 3″, and a GaNsingle-crystal film was grown by HVPE for 40 hours as described below.

In a mixed gas atmosphere in which the partial pressure of the H₂carrier gas was 6.00×10² Pa, the partial pressure of the N₂ carrier gaswas 8.29×10³ Pa and the partial pressure of the NH₃ gas was 1.13×10⁴ Pa,the temperature of the reaction chamber was raised to 1040° C. and heldfor 1 minute.

Growth of the GaN single-crystal film by HVPE was begun as describedbelow.

After holding the temperature for 1 minute as mentioned above, thepartial pressure of the GaCl gas was increased from 0 Pa to 3.54×10² Paand the partial pressure of HCl gas was increased from 0 Pa to 6.00×10¹Pa for 1 minute. The partial pressure of the H₂ carrier gas, after beingheld for 1 minute as mentioned above, was increased from 6.00×10² Pa to4.00×10⁴ Pa over 1 minute.

In the subsequent single-crystal growth step, the growth pressure to theend of growth was set to 1.01×10⁵ Pa, the partial pressure of the GaClgas was set to 3.54×10² Pa, and the partial pressure of the NH₃ gas wasset to 1.13×10⁴ Pa. Following completion of the single-crystal growthstep, the temperature was lowered to room temperature and a GaN crystalwas obtained.

No abnormal growth was observed in the resulting GaN single crystals,which were crack-free. The growth thickness was about 4.3 mm in them-axis direction (for the top and back faces combined) and about 7.0 mmin the [11-24] direction, Hence, in spite of the fact that the growthconditions were the same, differences in the growth rate depending onthe planar orientation were confirmed. The growth rate in the [11-24]direction was 175 μm/hr, and was thus confirmed to be at least 1.5 timesfaster than the growth rate in the principal plane direction.

In a wing growth region of the resulting GaN crystal, an approximately1.2 mm thick growth portion was sliced in a principal plane having amisorientation angle of 5° in the <000-1> direction from the (10-10)plane. The GaN crystal was further polished using a diamond abrasive andsurface polished by chemical mechanical polishing (CMP), therebyproducing a 400 μm thick free-standing GaN substrate 4″ whose principalplane has an off-angle of 5° in the direction of <000-1> from (10-10)plane.

The physical properties of a portion of the GaN self-supportingsubstrate 4″ thus produced and located about 5 mm away from the originalseed in the [11-24] direction were evaluated in the same way as inExample 1.

A reciprocal lattice map of the (100) plane when x-rays entered in adirection perpendicular to the a-axis was measured. In the Qx directionprofile that includes a maximum intensity and is derived from anisointensity contour plot obtained by such mapping, the width at thefoot of the peak (Qx width) was estimated.

The Qx widths at 1/300th and 1/1000th of the peak intensity wererespectively 3.68×10⁻⁴ (rlu) and 7.10×10⁻⁴ (rlu), which were very smallvalues.

As in the reciprocal lattice mapping measurement described above, thex-ray beam was made to enter from a direction perpendicular to thea-axis, and the (100) rocking curve (Open detector) was measured. Thefull width at half maximum of the peak intensity and the spectral widthsat 1/300th and 1/1000th of the peak intensity were respectively 109.6arc-sec, 500.4 arc-sec and 936.0 arc-sec.

Next, the GaN self-supporting plate 4″ was rotated 90°, the x-ray beamwas made to enter from a direction perpendicular to the c-axis, and the(100) rocking curve (Open detector) was measured. The full width at halfmaximum of the peak intensity and the spectral widths at 1/300th and1/1000th of the peak intensity were respectively 28.3 arc-sec, 216.0arc-sec and 417.6 arc-sec.

The spectral width of (100) XRC when the x-ray beam entered from adirection perpendicular to the a-axis was divided by the spectral widthof (100) XRC when the x-ray beam entered from a direction perpendicularto the c-axis, and the ratio of these was calculated. The ratio for thefull width at half maximum of the peak intensity and the ratios for thespectral widths at 1/300th and 1/1000th of the peak intensity wererespectively 3.88, 2.32 and 2.24, indicating that the anisotropy wassmall.

Also, an undoped GaN layer was grown to 1 μm by MOCVD on a GaNself-supporting substrate 4″, and evaluation of the stacking faultdensity by cathodoluminescence (CL) measurement was carried out,yielding a result of 1.6×10³/cm. The stacking faults observed by CL atthe surface of the m-plane had lengths in the a-axis direction that wereat least 200 μm.

Comparative Example 2 Crystal Growth Directly on Seed Crystal

A comparative GaN self-supporting substrate 3 having a rectangular shapemeasuring 5 mm in the <0001> (c-axis) direction and 25 mm in the <11-20>(a-axis) direction, and having the (10-10) plane as the principal planeand a thickness of 330 μm was produced from a (0001) plane bulk crystalobtained by the same method as in Example 9. The comparative GaNself-supporting substrate 3 was placed on a PG plate and, as describedbelow, a GaN single-crystal film was grown by HVPE for 40 hours.

In a mixed gas atmosphere in which the partial pressure of the N₂carrier gas was 8.29×10³ Pa and the partial pressure of the NH₃ gas was1.13×10⁴ Pa, the temperature of the reaction chamber was raised to 1040°C. and held for 1 minute.

Growth of the GaN single-crystal film by HVPE was begun as describedbelow.

After holding the temperature for 1 minute as mentioned above, thepartial pressure of the GaCl gas was increased from 0 Pa to 3.54×10² Paand the partial pressure of HCl gas was increased from 0 Pa to 3.48×10¹Pa for 1 minute. The partial pressure of the H₂ carrier gas, after beingheld for 1 minute as mentioned above, was increased from 0 Pa to8.22×10⁴ Pa over 1 minute.

In the subsequent single-crystal growth step, the growth pressure to theend of growth was set to 1.01×10⁵ Pa, the partial pressure of the GaClgas was set to 3.54×10² Pa, and the partial pressure of the NH₃ gas wasset to 1.13×10⁴ Pa. Following completion of the single-crystal growthstep, the temperature was lowered to room temperature and a GaN crystalwas obtained.

No abnormal growth was observed in the resulting GaN single crystaldirectly on a seed crystal; the GaN single-crystal was crack-free. Thegrowth thickness was about 4.3 mm in the m-axis direction (for the topand back faces combined).

A 1.2 mm thick growth portion of the resulting GaN crystal was sliced ina principal plane having a misorientation angle of 5° in the <000-1>direction from the (10-10) plane. The GaN crystal was further polishedusing a diamond abrasive and surface polished by chemical mechanicalpolishing (CMP), thereby producing a 400 μm thick free-standing GaNsubstrate 4 whose principal plane has an off-angle of 5° in thedirection of <000-1> from (10-10) plane.

The physical properties of the GaN self-supporting substrate 4 thusproduced were evaluated in the same way as in the working examples.

A reciprocal lattice map of the (100) plane of the comparative GaNself-supporting substrate 4 when x-rays entered in a directionperpendicular to the a-axis was measured. In the Qx direction profilethat includes a maximum intensity and is derived from an isointensitycontour plot obtained by such mapping, the width at the foot of the peak(Qx width) was estimated.

The Qx widths at 1/300th and 1/1000th of the peak intensity wererespectively 2.57×10⁻³ (rlu) and 4.7×10⁻³ (rlu), which were very largevalues.

As in the reciprocal lattice mapping measurement described above, thex-ray beam was made to enter from a direction perpendicular to thea-axis, and the (100) rocking curve (Open detector) was measured. Thefull width at half maximum of the peak intensity and the spectral widthsat 1/300th and 1/1000th of the peak intensity were respectively 154.4arc-sec, 1782 arc-sec and 3420 arc-sec, which were very large values.

Next, the comparative GaN self-supporting plate 4 was rotated 90°, thex-ray beam was made to enter from a direction perpendicular to thec-axis, and the (100) rocking curve (Open detector) was measured. Thefull width at half maximum of the peak intensity and the spectral widthsat 1/300th and 1/1000th of the peak intensity were respectively 32.5arc-sec, 334.8 arc-sec and 514.8 arc-sec.

The spectral width of (100) XRC when the x-ray beam entered from adirection perpendicular to the a-axis was divided by the spectral widthof (100) XRC when the x-ray beam entered from a direction perpendicularto the c-axis, and the ratio of these was calculated. The ratio for thefull width at half maximum of the peak intensity and the ratios for thespectral widths at 1/300th and 1/1000th of the peak intensity wererespectively 4.75, 5.32 and 6.64, indicating that the anisotropy wasvery large.

Also, an undoped GaN layer was grown to 1 μm by MOCVD on a GaNself-supporting substrate 4, and evaluation of the stacking faultdensity by cathodoluminescence (CL) measurement was carried out,yielding a result of 9.2×10⁴/cm, which was a very large value. Thestacking faults observed by CL at the surface of the m-plane had lengthsin the a-axis direction that were at least 200 μm.

Reference Example

A reciprocal lattice map of the GaN self-supporting substrate 1 on whichthe above C-plane growth had been carried out was measured in the sameway as for the GaN self-supporting substrate 2, and the width at thefoot of the peak (Qx width) was estimated. The Qx widths at 1/300th and1/1000th of the peak intensity were respectively 1.45×10⁻⁴ (rlu) and2.00×10⁻⁴ (rlu), which were substantially the same values as thoseobtained for the GaN self-supporting substrate 2 in this example. Aperiodic table Group 13 metal nitride crystal that has been C-planegrowth is a crystal without stacking faults. Hence, it can beappreciated that, although the periodic table Group 13 metal nitridecrystal of the invention has been crystal-grown using a non-polar planeas the principal plane, the number of stacking faults has decreased.Moreover, it can be appreciated that this is a crystal which, along witha decrease in the number of stacking faults, has little crystal warpage.

The anisotropy of the x-ray rocking curve was measured for the GaNself-supporting substrate 1.

Measurement was carried out in the same way as in the working examples.When x-rays were made to enter perpendicular to the a-axis, the fullwidth at half maximum of the peak intensity and the spectral widths at1/300th and 1/1000th of the peak intensity were respectively 35.0arc-sec, 194 arc-sec and 323 arc-sec.

When x-rays were made to enter perpendicular to the c-axis, the fullwidth at half maximum of the peak intensity and the spectral widths at1/300th and 1/1000th of the peak intensity were respectively 30.9arc-sec, 176 arc-sec and 299 arc-sec.

The spectral width of (100) XRC when the x-ray beam entered from adirection perpendicular to the a-axis was divided by the spectral widthof (100) XRC when the x-ray beam entered from a direction perpendicularto the c-axis, and the ratio of these was calculated. The ratios for thefull width at half maximum of the peak intensity and ratios for thespectral widths at 1/300th and 1/1000th of the peak intensity wererespectively 1.13, 1.10 and 1.10.

This application claims priority from Japanese Patent Application No.2012-081735 and Japanese Patent Application No. 2012-082153, filed onMar. 30, 2012, the entire contents of which are incorporated herein byreference.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

EXPLANATION OF REFERENCE NUMERALS

-   100 Reactor-   101 Carrier gas introducing pipe-   102 Dopant gas introducing pipe-   103 Group 13 starting material reservoir introducing pipe-   104 Nitrogen source introducing pipe-   105 Group 13 starting material reservoir-   106 Heaters-   107 Susceptor-   108 Exhaust pipe-   109 Base substrate-   G1 Carrier gas-   G2 Dopant gas-   G3 Group 13 source gas-   G4 Nitrogen source gas

The invention claimed is:
 1. A gallium nitride single-crystal substratehaving a thickness of 0.2 mm or more and comprising a gallium nitridecrystal grown on a non-polar or semi-polar plane of a gallium nitride,wherein, a first value calculated by dividing the width at 1/300th ofpeak intensity of a (100) rocking curve obtained when x-rays enter thegallium nitride crystal perpendicular to the a-axis, by the width at1/300th of peak intensity of a (100) rocking curve obtained when x-raysenter the gallium nitride crystal perpendicular to the c-axis is 3 orless.
 2. The substrate according to claim 1, wherein the first value is1.12 or more.
 3. The substrate according to claim 1, wherein a secondvalue calculated by dividing the width at 1/1000th of peak intensity ofthe (100) rocking curve obtained when x-rays enter the gallium nitridecrystal perpendicular to the a-axis, by the width at 1/1000th of peakintensity of the (100) rocking curve obtained when x-rays enter thegallium nitride crystal perpendicular to the c-axis is 3 or less.
 4. Thesubstrate according to claim 3, wherein the second value is 1.15 ormore.
 5. The substrate according to claim 1, wherein a third valuecalculated by dividing the full width at half peak intensity of the(100) rocking curve obtained when x-rays enter the gallium nitridecrystal perpendicular to the a-axis, by the full width at half peakintensity of the (100) rocking curve obtained when x-rays enter thegallium nitride crystal perpendicular to the c-axis is 4 or less.
 6. Thesubstrate according to claim 5, wherein the third value is 0.98 or more.7. The substrate according to claim 1, wherein the number of stackingfaults visible in cathodoluminescence imaging is 3×10³/cm or less. 8.The substrate according to claim 1, wherein a c-axis misorientationangle distribution at a distance of 40 mm is within ±0.5°.
 9. Thesubstrate according to claim 1, which is a gallium nitridesingle-crystal self-supporting substrate.
 10. The substrate according toclaim 1, wherein the gallium nitride single-crystal substrate thicknessis 0.3 mm or more.
 11. The substrate according to claim 1, wherein thegallium nitride single-crystal substrate thickness is 0.4 mm or more.12. The substrate according to claim 1, comprising a gallium nitridecrystal grown on a non-polar plane of the gallium nitride.
 13. Thesubstrate according to claim 1, comprising a gallium nitride crystalgrown on a semi-polar plane of the gallium nitride.
 14. The substrateaccording to claim 1, wherein the gallium nitride crystal is grown byhydride vapor-phase epitaxy.
 15. The substrate according to claim 12,wherein the gallium nitride crystal is grown by hydride vapor-phaseepitaxy.
 16. The substrate according to claim 13, wherein the galliumnitride crystal is grown by hydride vapor-phase epitaxy.
 17. Thesubstrate according to claim 1, wherein the Qx width at 1/300th of peakintensity is 4×10⁻⁴ rlu or less.
 18. The substrate according to claim 1,wherein the Qx width at 1/300th of peak intensity is 3×10⁻⁴ rlu or less.19. The substrate according to claim 1, wherein the number of stackingfaults visible in cathodoluminescence imaging is not more that 1×10³/cm.20. A semiconductor device comprising the substrate according to claim9.